1 00:00:02,780 --> 00:00:05,679 alright let's get started if you haven't already there's two handouts on the left and I should take two pieces of paper so we'll be doing some actual origami folding we'll be folding six eight four nine today just like this it will only take us eight hours or so this is the Jenny and Eli folding you've seen on the coaster pretty awesome now we'll be folding butters more like this so thanks everyone for giving so many cool questions and comments and the feedback is really helpful I was I didn't know what I was gonna cover in this class I had too many ideas and your questions really help narrow it down into exciting things so the structure is gonna be I'm gonna go through questions so it's a funny kind of interactivity where there's a whole day in between where you ask the questions and where I answer them but feel free to ask more questions follow up things but there's a lot already here so it should be fun these are not questions but sort of funny er comments if you like double rainbow jokes this was this this lecture happened like a couple of months after the double rainbow fiasco there's a lot more as I recall it was sort of a running theme throughout the whole semester so look out for that I know this is gonna this is entertaining I'm getting used to listen to myself at double speed should be fun this class definitely is nice in the way that with fairly simple technique you can prove a very powerful theorem and that's sorry I just remembered I need to push a different button here that's that's hopefully a theme throughout the class but definitely especially nice here so it's kind of cool though strip folding if it was an open problem for a couple years at least and no one thinking how do we fold any shape that seems really tough the point of this the strip folding approach is that once you have the right idea just start with a really long rectangle somehow it becomes easy there's still a lot of details and getting that to work but it's kind of neat how that that works out and now we get to actual all proposals so folding practice planning on doing this but it's an explicit comment to that effect so we're going to fold some letters of the alphabet you have in your packet instructions for making the individual digits six four eight and nine and you also have which are all pretty easy you also have a diagram for it's crazy design called typeset which can desync this same folding can make any letter of the alphabet and any digit so just to show you what they will look like these are my foldings of six eight four and nine according to the first set of diagrams and then this is my folding of think the letter the number six rather out of jason coos design so if you wanted to reconfigure it to i guess eight is kind of hard let me do four think okay so four four I've got a fold this guy under fold this here this tab I think goes back here so the advanced origami folders can definitely do in this classic and if they do the Jason coos design but it it takes a little while I think there I've got a four got it a little hard to hold in position but at least in theory it will make any letter all out of one one folding you just have to move all the tabs around so it's kind of neat but it takes at least half an hour so to fold that unless you're really fast so I would recommend pick one of these working groups if you like if you want you can form a group of 4 and make 6 8 4 & 9 follow the diagrams this is an exercise in following diagrams one way or the other only have time to maybe make one digit each but have fun with it and if you have questions raise your hand I can tell you the first step in 6 8 & 9 is to make an 8x8 grid there's a lot of ways to make an 8x8 grid but an easy one is shown here so you take your your sheet you fold the bottom edge to the top edge I think they want to do it white side up again so they're all valleys when you align those edges you'll get a nice bisector then you repeat folding the bottom edge to the middle and once you do that to save a little bit of time you can then fold that new bottom edge to the middle again that will do eights on one side it's a little bit inaccurate because you're folding through two layers but it's a little faster time is of the essence then you do the same thing on the bottom and you'll get ates in one dimension but then you have to fold it in eighths in the other dimension once you have eighths it's like three steps it's really easy four six eight and nine four uses a different approach it's a little more free hand if you want to be more creative try the four you've got to kind of eyeball what looks and feels good for number four so out of curiosity how many people have an 8x8 grid at this point you want to take full so that's the top half of these diagrams to 8x8 grid then it's mostly folding up over individual edges and some corner folds but they're all they're all simple folds in this world so you're folding through I think always all the layers on this this is only folding through one layer but these would always fall into the some layer simple folds category so for example make a six this bottom edge up fold the left three squares over this corner up fold this corner down fold this down this over there's really big six and these numbers are all pretty much proportioned correctly the four you have to be it helps to have a reference model one of the other digits to make it the right height but it'll end up roughly correct anyway it's a little bit narrow and it's designed it's slightly narrower than the six and the nine but otherwise they're nice compatible digits there's a whole alphabet on the website that's linked from this slide so you can go check it out the origami Club so it's kind of fun to think about font design and alphabet design there's actually a lot of origami alphabets out there this is one of the simplest that has digits anyone have questions how many people folded a letter a digit okay so maybe I will you can keep folding but maybe I'll continue on it's gonna be a lot of fun crackling anyone folded this one anyone working on it uh-huh a bunch of people cool well let me know when you finish it's kind of fun it's not that hard I wanted to point at the origami website or gham it is the origami Club at MIT and at the top you see a different alphabet this is a four fold alphabet designed by Jeannine Mosely who's an MIT alum and came to this class two years ago and so that's the reference design in 2002 I'm not sure if it has digits though at least the the diagrams we found for the letters do not also have digits so I think an interesting challenge is to design a for fit for fold digit set to compliment her letter set if you're interested that could be a cool project to work on folding design minimal fold alphabets you could try a three fold alphabet to fold alphabet whatever also on this website are the meeting schedule it's always Sundays sometimes two sometimes three o'clock check it out and there's a convention coming up our very own origami convention on October 27th and Jason ku wanted me to to remind you about that coming up so if you even if you've never done origami before other than today you should check it out it'll be fun lots of different sessions on from simple models to complicated models this is a cool design by Brian Chen another MIT alum it's one square paper folded into the men's at Montes logo but here instead of the oil lamp you've got a little origami crane cool stuff cool so we proceeded on to other questions this is a pretty simple one at the top of the note says folding any shape aka silhouette folding and gift wrapping it has a couple of references so where do those terms come from it's the question and one answer is it's the title of the paper folding flat silhouettes and wrapping polyhedral packages but that's that's not the real answer so this is the two of us and Joe Mitchell it's also that I think the introduction of the term computational origami but those those terms come from earlier references so in that paper there's a sentence classic open question origami mathematics and we don't really know where it came about but it was first formally posed by Bern and Hayes in this soda 96 paper which we'll be talking about in the next lecture lecture three and this is a quote from their paper is every simple polygon when scaled sufficiently small the silhouette of a flat origami the point of saying the word silhouette is that when you fold something like this number six there's a whole bunch of layers and there's a lot of complexity to this folding by saying silhouette we just mean you know collapse all the layers ignore the coloring and just take the outline so the silhouette of this thing is a rectangle and in general that's the sort of the transformation to throw away the complexity of the folding and say I just care about the shape can I get the desired shape there's some other interesting questions here though which haven't been fully addressed how many creases are necessary to fold well actually to that in a later question how thick must the origami be this the strip method can shows that if you start from a rectangle of paper or the number of layers can be very small I think 2 or 3 is enough for all the gadgets that we use probably 3 if you start from a square though we don't know the answer to that question and in practice folding through many layers is tough yeah so that was the silhouette problem and then the gift-wrapping problem and the motivation is you have a weird-shaped gift you want to wrap it with a piece of paper and this is posed to us in a talk by Janaki Amma at a Canadian geometry conference jun akiyama is really cool guy he he has a math or has had for many many years on mathematics TV show in Japan and he's known throughout Japan because everyone in school watches his videos and it covers really interesting mathematics some of the results in this class are actually in his videos as well it's mostly in Japanese so it's a little hard to for most of us to watch but there's some subtitle versions and they're really fun maybe we can have a movie night and watch one of them I get permission so there isn't a great reference for that I mean written some papers about different kinds of wrapping problems but mostly it was this talk that he gave in 1997 which is when I was just starting out in computational geometry that's where the terms come from a lot of words have you ever actually folded a model using this method of zigzagging and folding with this strip any real or sensible or pretty origami models or is it purely for the sake of universality my knee-jerk reaction was no way is is practical this is just for universality and the point of this theorem has always been in my mind to prove that everything is possible but then the challenge is to find good foldings for some notion of good but actually there is a lot of strip or there's there a bunch of examples of strip folding not a lot of different folds and not terribly many gadgets but there's some cool things especially with strip weaving these are just a few examples of woven colored strips you can make fun things like space invaders you can weave together baskets and do wrap your packages and so on so this is a little bit more bar gammak so there were no real folds in there except at the edges of the cube this one is a modular origami it involves a bunch of different folds to get the all the pieces to lock together modular origami means you have a bunch of identical pieces so they kind of weave together through folding and then you can make a nice little crown this is a very classic model you've probably seen it at some point here that the paper is slit and then it's woven so but there is there's some folds down here so not a lot of folding but strips are pretty neat you can definitely use them all sorts of different designs here's some more sculptural design ii models from taking strips of paper this has no glue in its I think there's more strips at the end lock locking this together and this guy Zachary footer ur2 took a bunch of these kinds of units and started weaving them together and make really complicated shapes so you can definitely do cool things with strip folding and another sort of common one around these days is taking gum or candy wrappers and weaving them to get folding them down into little strips and then weaving them together to make handbags and other things become kind of a fashion trend over the last few years so those are things you can do with strips we have used it in one paper that's where the goal is actually to be efficient and use a small piece of paper and not just prove some universality result this is in our paper folding a better checkerboard which we will talk about I think in two lectures if I recall correctly in more detail but this is sort of a baseline this is not the better method just to develop in this paper but it's sort of the starting point which is you take a square so this actually starts with a square you do this pleating and you get this this is with bicolor paper it's dark on one side light on the other you get this strip of squares in color pattern and then you take that strip a huge number of layers in the middle so it's not super practical but it's actually pretty efficient in terms of how big a square you start with too an n-by-n this is obviously not to scale you need more squares here in order to make this thing and then you just sort of snake your path back and forth you could use turn gadgets or here we're just using 45-degree folds and this is pretty close to what was believed to be the best way to fold a checker board and then this paper shows how to do a factor of two better so we'll talk about that later but there are some uses for strip folding this is a little bit theoretical but it's actually pretty competitive against the best end by end checkerboard foldings in the origami world like the one I showed last class so that's practicality of strip folding next questions more about strip folding there are a couple things that are in the lecture notes the handwritten lecture notes but we're not even mentioned in the audio part of the lecture so a few people asked about what what are these things said pseudo-polynomial upper bound pseudopolynomial is a fun term let me tell you a little bit about it that's from the algorithms world but even a lot of alguns people don't know it so let me tell you so maybe first I should tell you about polynomial in general what these terms are about is measuring how fast an algorithm is so the idea is you plot conceptually n this is the problem size so if you wanted to fold an arbitrary polyhedron the one way to think of the problem size is the number of vertices edges and faces just the the total number of things you're given as input and then your output is whatever but n is supposed to be the input problem size and then on the y-axis you want to do you want to plot running time of your algorithm so this is how long it takes to compute the way to fold your square paper into your desired shape and generally this is going to increase and the question is does it increase in a reasonable way or in a crazy way you know that goes exponentially so you want to know how does the running time grow with n polynomial is a sense of good growth and it just means you grow like n to the C where C is some constant so ideally you'd have n or maybe you have N squared or n cubed or n to the fourth all these are considered good running times not quite as good as polynomial is pseudo polynomial and I would conjecture for this problem of folding an arbitrary given polyhedron you cannot achieve a polynomial number of folds let's say so there are two things we could measure here the running time the algorithm we could measure actually three things we can measure the number of folds you make number of operations you do sort of on the paper and a third thing would be scale factor how big a square do I have to start with in order to make desired polygon and pseudopolynomial means n times R to the C what's R R is some geometric parameter geometric ratio in the input and in particular for this problem what makes sense for our is basically the longest length divided by the shortest length this is typically what R refers to this will come up in later lectures as well so for example you take your entire shape you measure the sort of the diameter of the shape the two farthest points that's your longest length shortest length would be maybe you have a triangle something like this in this target poly huge and you want to make this would be your shortest distance this is actually called the minimum feature size in computational geometry or the minimum altitude of any of your triangles okay so that's just some number and you know you can have a triangle just super super narrow and so it's this ratio are could be arbitrarily large even though you only have three vertices three edges one face so N&R are not necessarily comparable so that's why in pseudo polynomial we put them both together and then we raise them to some constant power that's a pseudo polynomial running time so the the the question is being posed here is can you get a pseudo polynomial upper bound and can you get a pseudo polynomial lower bound and it doesn't say for what but it's for all three problems running time number folds scale factor and not all of these are open so in the original paper there's this theorem that says lots of things you know you can fold anything and it says here the folding requires a number of folds polynomial and N and the ratio R so it already claims that there is a pseudo polynomial bound on the number of faults it doesn't say what that pseudo polynomial bound is is it n times R is it n plus R is it n times R squared I would guess one of the first two and times RN plus R so that's the upper bound question maybe we can work on this in a problem session a lower bound question is do you prove that you need some dependents both on N and R which I would guess is pretty easy if you want to take a square and fold it down to a really really skinny triangle I think you need at least our faults roughly and similarly should need a at least n folds so there should be a lower bound of like n plus R but none of these have been written down explicitly so that's what those open questions are then there's another slide 6 which is completely uncovered it's not me if they're questions I should maybe take a brief moment to breathe so the next part of the lecture notes s about seam placement so seam placement it's the following kind of issue when you fold like this number it's a six this is a nine-fold this number nine in addition to seeing the color pattern if you look closely there's also these kinds of seams this white square is not just a white square you can see on the top layer this crease line and here there's a seam here this the seam these are like visible lines of course you have to have seams at the color transitions but there's other seams as well maybe you want to minimize those seams you want to get you want to place the seams in a cool pattern when you fold checker boards there's a such thing as a seamless checker board where every square is a whole square paper there's no visible crease lines on the top layer so this is an extension of the universality result to also get sort of universal seam placement and what what the original paper proves is that you can place the seams as long however you want provided the seam regions the regions between the seams are convex polygons which is almost always the case you look at a typical model you know here this the seam regions are all rectangles and triangles so this could you could you could achieve exactly the same pattern if you wanted it you could also say oh well here's a nice rectangle I'll make that a seam region here's a nice rectangle make that a seam region but you could not make the entire number 9 here a seam region because it's non-convex least you can't do it with this technique we don't know necessarily whether this is possible by some other folding I would guess no but it is possible to make some non convex seam regions for example I could take this page and fold the corner over and now I've got a non-convex seam region here so some non convex seam regions are possible open question is what seam what if I give you a polygon we know every polygon is possible now I give you a polygon and I subdivide it into seam regions which of those are possible not everything is possible I'm pretty sure though I'm not sure we have a proof of that some things like this little heart shape are possible characterized this is another cool possible problem for a problem session questions about that okay so ah I have a little bit about the proof of how this is done if you wanted to just do convex regions so the general approach here for is you we want to visit all of the regions in some order this is called a tour it's pretty easy to just I mean you're allowed to visit regions more than once so you just keep going keep trying to visit some unvisited seem region when you visit a seam region it's a convex polygon so what we're gonna do is make our strip fairly wide actually wide enough to completely cover that seam region then at this moment we'll basically need to turn to do the next one and so there's we know how to sort of change the direction of this strip using a turn gadget then we have to change the width of the strip maybe it needs to be wider maybe it needs to be thinner and then we need to shift the strip one one way or the other so you know if we just end here we turn we might be misaligned so we need to shift it over expand it then do the next one then turn then shift it over then set the right width keep going like that okay that's pretty messy and complicated but you can do it with these two gadgets strip with gadget you take a strip and you can make it anywhere between 1/2 and 100% of its original width so the idea is you start with a really wide strip wide enough to cover all the polygons then you do this gadget and keep shrinking it by half until it's roughly the right size and then when you're almost correct you shrink it by a little bit more here drinking to 1/3 and then you get your shrunken strip and it happens right at the the line that you specify so you can basically on a dime shrink your strip and then by doing the reverse you can grow it back this is maybe not with simple folds though then the other gadget is a shift gadget where you're just you're at this position you want to shift up so that's pretty easy you just do to turn gadget it's okay so that's how at a high level how that making a desired seam pattern works go on to the next question a lot of people asked about this and so this is an open problem that I mentioned orally it's not written in the notes which is can you actually do the things that we said we can do with simple faults so can you get a universal folding of a polygon to color pattern polyhedron using simple faults and I thought it would be fun to actually work on this here live because I think this is an easy problem and there's a bunch of possible answers and there are even two suggested ideas from the comment skill so let me just remind you of the issue what's happening and then I need your input what's gonna work here so general picture for strip method was we do one triangle we end here then we do a bunch of folds like this and then we and here maybe and then we sig zag and the trouble is we've already made this triangle over here when we make this triangle we have this excess stuff which I haven't drawn very accurately but you recall it looks something like that or maybe even more like that if we use right angle turn gadgets and then we want to fold it underneath and we're doing that the way I said with hi gadget Mountain folds but the model of simple Falls which I should make may be more explicit you're not allowed to collide during the motion it's the idea with the simple fold is that you should be folding along one line segment and you should fold by the model that we defined back in the day I'll I'll talk more about where this notion comes from you fold by plus or minus 180 degrees which means after you do the fold you'll be flat again and no collision during the motion so if we folded this triangle and then we folded this one and this stuff is on the top we can't mountain fold that's not considered a simple fold now one proposal is could we just make the next triangle underneath the previous one a different proposal is Valley fold these are actually different proposals because especially for two color patterns it'll make a difference if we weave Valley fold here there's gonna be some junk on the front side especially if you want to get a desired seam pattern but maybe we'll leave seam patterns for later if you want to get a color pattern you might reveal some wrong color when you do that Valley fold so I haven't really thought about this idea yet I think it might be good so the idea there would be so you've already made this triangle you've out you Mountain fold everything now when you go when you do these zigzags you want to be underneath everything that you've done yeah okay different idea as you basically fold this out of the way do this thing hide gadget and then fold it back maybe I've wondered about that too it's it's gonna get a little challenging them in general there's a huge set of triangles so unless you can like go far away make your triangle and then plop it down maybe it's possible ah I guess we can pursue that idea but maybe first we should exhaust the easier ideas so I mean that is definitely plausible that's possible doing that with simple folds and not leaving any garbage is gonna be a little challenging but might be doable this to me is the simplest idea so we should first see if it works anyone see problems with this plan so guess we should think about I have some strips we could think about what it means to be doing a turn gadget underneath here so I don't know quite about well let's suppose we're already here and now maybe I do some as a turn gadget goat some mountain folds then a at 90 degrees and then a valley fold like that and then I do a mountain fold I think it might be okay because turn gadgets start with a mountain fold which so if you're underneath everything that's gonna avoid collision and then the valley fold is brings it back with again we're using just the space below everything that we see so then we make that strip we keep turning around and then later on we're going to mount and fold this behind somehow to meet this edge no seams okay yeah question yeah going from one triangle to next yeah so we could think about that too it's it's very you're right I mean I'm just looking at the turning-around part for making a single triangle but there's also the turn gadget going from here to here it's actually slightly more complicated that we've covered in class but not really much it's just a slightly generalized trend gadget so you're coming here you basically want to turn around so but let's just think about a way to do it you could imagine first doing a turn like this it's not exactly a pure turn gadget and then turning around to get to the next place this is really hard to do on a blackboard strips just tend not to stay together very well okay now we're going parallel to the correct direction then we turn back and forth but each of those is just using turn gadgets so as long as the turn gadget works fine a turn gadget is gonna be a mountain fold we're just gonna go behind everything and then a valley fold to bring it to a desired direction those are all using everything behind the board so it seems like all those operations are okay now we should also check the color reversal gadget which it's funny thing I remember everything I did before 2000 or so so I still have memorized the color reversal gauge at least I think so I should probably color this piece of paper so you can see the colors change I don't remember anything I've done since 2000 but anything up to 2000 I'm okay this is 1998 I think I remember falling Lots this is ticker tape they use for or not ticker tape but just use this for like adding machines so I think it's a 90 degree mountain fold then you fold up like that and then you fold back down with a mountain fold like that and you get a color reversal on all of those folds were working behind my plane here so should avoid collision with everything I think you can do color reversal and turn gadgets behind and so this suggestion works who made this suggestion good idea so unless there any objections I think that will work I had a different plan which was to use this second idea and set up the turn gadget so there was no when you fold this with a valley fold there's no ugly colors so you could maybe modify the turn gadget to be completely solidly colored on both sides but I think this is much easier it's probably why I didn't write it down the notes but I'm not sure yeah go far away make a triangle okay how do you do that last part what's so I mean you have to do it with simple folds that's the main that's the challenge so the idea is you you're way out here you have a triangle out here which you want to bring over here maybe I should do it like this so you could do something like this so now the triangles over here then maybe you want to go most all the way here and then fold it back and then fold it forth and back until you get your triangle exactly where you want it it seems possible my only concern would be when you do this thing there might be a little little corner depends how you fold this thing and then you've got to hide that corner and if there's triangles all around here there may not be room I mean maybe there's triangles all around here it's okay to have that corner but maybe the triangles are different colors so I I do believe that should be possible it's but I think it is a little bit more complicated because you have to hide one last piece after you get it in position anyway I think there are at least three ways to solve this problem yeah are you allowed to unfold it's a good question I don't remember whether the original model says whether you're allowed to unfold so there are two versions simple folds and unfolds or just simple folds I don't think we actually said unfolding is allowed so we're definitely thinking about at some point it's probably not in the model as defined there questions all right what's next this is the paper that introduced simple folds it's called when can you fold a map because it originally was motivated by a map folding and it had a bunch of reasons for introducing simple folds among them here's this quote which if you've watched l1 as in there I think the easiest way to refold a road map is differently coalesce to make it easier to refold your road map correctly but here's one quote from that paper as motivation so is origami motivation but we're also wondering about applications like sheet metal bending cardboard folding things like that where you want to manufacture things using a machine and while origamist can do complicated folds non simple folds to make artwork practical manufacturing you want to have the simplest possible machine so if you can get away with just simple folds as defined here that would be great now you don't really need some of these are maybe artificial you probably don't need the 180 degree condition because most of the things you want to fold aren't flat we introduced that just to keep things simple mathematically but you'd like to fold along just one segment at a time ideally you definitely don't want collision so you don't want the material to hit things whereas in origami you can do tuck so you can do things that you know are not simple folds it's a lot harder with a machine that doesn't have any feedback so here's a very simple machine this is a a break folder we actually have a break folder in CC although this one is electro break so this has an electric assist so the idea is you slide your sheet in and you hold here you pull up and in this case is bending to a 90 degree angle but you can adjust it to different angles and so on so that and there are lots of automated machines a little hard to get photos and videos of them but they're based on this principle maybe you you push in a V and you end up with a crease in one spot and you'd like to just make sort of conveyor belt with lots of different pushes and pulls and do a bunch of simple folds basically except for this 180-degree constraint and so we're just curious about what's possible by simple folds and that led us into the mat folding stuff where it's fairly easy to characterize other things where it's harder which we'll see in lecture 3 I thought I'd show you some examples of things people make with pretty much simple folds other than this 180 condition out of things like this is folding wood so you take sheet material and you start bending these parts up and you can make a little chair a little table and you can fold it back when you're not using your living room you can hide everything so you could imagine also having multiple sheets and sometimes your room is a living room other times it's a whatever furniture you need you just unfold the appropriate thing it's kind of a vision here's a cute little folding card there's a huge number of folding chairs but this one is pretty much simple folds the one thing I'm not sure where there falls under simple fold is this fold so it's you do fold along one line but it's in two different pieces not sure we'd call that a simple fold there's of course lots of slits in the material here but of course it has all the same advantages of simple folds this is easy to execute one step at a time here's some more complicated designs some of these are computer rendering some of these are real again too taking furniture out of flat walls here's some table designs these are of sheet metal I like I like this one it's very simple take a square of sheet metal put in some slits do some very simple folds boom you've got a table this one's also pretty simple here we again here we're folding along one line but it's in two different pieces so is that a simple fold is definitely harder to build such a machine but it's doable here we have something's definitely not a simple fold but it's also fairly easy to execute using our roller you can kind of curve one segment so I mean when you go to reality there's you can change the model in all sorts of different ways and still have something practical and no one rule set is is gospel but mathematically we have to hone in on at least one model at a time and then we can see how changing the rules changes what you can make okay next question this is actually about the definition of simple folds so it's probably answered already is allowed to bend the rest of paper to get it out of the way avoid collision the answer is no in simple folds at least you're you're only allowed to move that one segment we have actually lately been thinking about a different model where you do allow this but simple folds you can't move other parts you can just move the single hinge that you're folding and the end product has to be flat yes in our model though it'd be interesting to think without this condition because you're doing 180 degree operations before you do the next one you will be flat at all times 1d or 2d according to whether you started with a 1d piece of paper or a 2d piece of paper okay so in then the second half of the lecture was basically about proving characterizing flat foldability of 1d segments and it showed in particular that simple folds are universal that you if you have some Mountain Valley pattern and it's foldable at all if it's flat foldable it will be flat foldable via simple folds and in particular using crimps and n folds so let me and there and it was a bit of a messy proof partly because I've made a mistake in lecture as you saw I kind of corrected for it on the fly but it's maybe not the best written so I wanted to go through a couple quick examples to make clear all the issues there so here are the ones I prepared we can certainly do more if it's still not clear so here's a simple Mountain Valley pattern and it's got some long segments and let's just say equidistant segments here 3 valleys than a mountain so first question is is this mingling and then this the ultimate question is is it flat foldable so is it mingling well maybe you can answer for me just yes or no 50% chance okay so maybe the definition of mingling is not super clear let me review it so you look at each I mean generally of a sequence of mountains and valleys so you look at a chunk of all valleys then you look at a chunk of all mountains and chunk of all valleys here there's only two chunks three valleys and one mountain and the definition is a little awkward for a single crease but let's start with the all valleys the point is to check for the first segment between two valleys versus the segments just before it which is bigger and this is the bad case this is the non mingling situation because this thing is bigger than this strictly bigger it's strictly bigger the notation we used and the lecture is an open square bracket so square bracket meant that this is bigger round bracket would mean this is less than or equal to this that's just the definition over on this side of the valleys this length is equal to this length so the last distance between two valleys is equal to the one right after it and so that's a good case so we write a closed round bracket then we have a sequence of mountains and here it's a little confusing but it's the same idea you look at so this is the very first mountain you look at the length right after it versus the length right before it and this is smaller and so that's a good case we write an open round bracket for this mountain group and then same thing now we're comparing the same two distances but it's now bad because this one is strictly longer than this one so we write a closed square bracket so that's the notation in this example any questions about that so you just have to check we're looking in general you have a whole group of valleys because these are all valleys or all mountains and you want to compare this one versus this one and it's square closed according to which is bigger and you want to look at the last one versus the after last one okay so that's the notation and the point of the proof was to argue that either there's a if you're gonna be flat foldable at all actually if you're mingling mingling meant that for each of these intervals at least one of the sides was round that was considered good so this crease pattern is mingling because there's two regions this one has a round bracket this one has a round bracket and what we argued is that if you're mingling you which was necessary if you're flat foldable you have to be mingling it's a necessary of a not sufficient condition for flat foldability if you're mingling either you have a pattern like this close round bracket open round bracket that's good because this is a crimp that you can do and you can see it up here this is a crimp you Valley fold mountain fold and you don't hide anything when you make that operation or there's an end fold which correspond it to an open round bracket at the beginning or a closed round bracket at the end so here there's a crimp let's do the crimp so when we do the crimp let's keep this part of the paper fixed so this we go over to here roughly then we valley fold then we mountain fold and we keep going from there it's that segment is that signal okay so we still have this this valley this was the valley we just folded this is the mountain we just folded now conceptually we just sort of fuse this back into the paper because those creases are done we don't need to think about them the point is in that region there were no extra creases this these round parentheses will guarantee there's nothing here no creases here here or here could be creases farther away but you buy these inequalities that this length is less or equal to this one and this length is less or equal to this one let's try greater than or equal to equal to then you know this is okay okay crimp so there's two valleys left so now we have two valleys we have a long segment in a long segment and this is something that can't be made because if you I mean there's no folded state of this thing never mind simple folds because it's gonna cross like that so this is not flat foldable yeah it's also not mingling because if you look at these two valleys you look at the distance over here that's bigger than this one so that's bad so you have an open square bracket and this one is also bigger than this imagining these is fused and so it's a closed square bracket and so this group of valleys is not mingling so it's not mingling so ultimately this pattern we started with is not flat foldable because one of the things we proved is that doing a crimp never changes flat foldability it's always a safe thing to do so I mean there was I mean you might wonder oh maybe there's some other fold I could do that eventually works but we proved crimps are always safe to do so and we did it and we got stuck that means this was not flat foldable even though it was mingling and so the mingling forever property just means if it's mingling and when you do a crimp and is still mingling and if you keep doing crimson it stays mingling all the way then you were flat foldable it's not a very satisfying characterization but it is a thing maybe I'll do one more example just to where it works we're super clear Oh out of time so I won't do another example all right ambitious yeah and I got to work on my timing there are a couple other fun questions here I would encourage you to read the notes about them in particular there's an algorithmic question how do you actually compute this efficiently you can do it very efficiently in linear time so and where C is one just n time instead of N squared or something using a pretty simple idea basically just look for the first crimp to do it and then see if they're crimps nearby and keep going forward and you can prove that takes linear time there is this fun question I enjoyed thinking about can you make any Mountain Valley pattern flat foldable by adding creases the answer is yes I can think of it as a puzzle there's one proposed way to do it here I have another one in the notes you can think about it and the last question is what is it possibly mean to fold something in four dimensions how do you imagine it hard to imagine but you can think about it you have a d-dimensional piece of paper you fold it through D plus one dimensions if you want to flat fold it it ends up back in D dimensions and your creases are D minus one dimensional and the rest you just have to visualize I have one example of folding a solid cube in half in the notes that's certainly possible it's not very well studied and there's lots of interesting open questions about higher dimensional folding any questions before we go all right watch lecture three and please send your feedback is really helpful you 2 00:00:05,679 --> 00:00:07,990 alright let's get started if you haven't already there's two handouts on the left and I should take two pieces of paper so we'll be doing some actual origami folding we'll be folding six eight four nine today just like this it will only take us eight hours or so this is the Jenny and Eli folding you've seen on the coaster pretty awesome now we'll be folding butters more like this so thanks everyone for giving so many cool questions and comments and the feedback is really helpful I was I didn't know what I was gonna cover in this class I had too many ideas and your questions really help narrow it down into exciting things so the structure is gonna be I'm gonna go through questions so it's a funny kind of interactivity where there's a whole day in between where you ask the questions and where I answer them but feel free to ask more questions follow up things but there's a lot already here so it should be fun these are not questions but sort of funny er comments if you like double rainbow jokes this was this this lecture happened like a couple of months after the double rainbow fiasco there's a lot more as I recall it was sort of a running theme throughout the whole semester so look out for that I know this is gonna this is entertaining I'm getting used to listen to myself at double speed should be fun this class definitely is nice in the way that with fairly simple technique you can prove a very powerful theorem and that's sorry I just remembered I need to push a different button here that's that's hopefully a theme throughout the class but definitely especially nice here so it's kind of cool though strip folding if it was an open problem for a couple years at least and no one thinking how do we fold any shape that seems really tough the point of this the strip folding approach is that once you have the right idea just start with a really long rectangle somehow it becomes easy there's still a lot of details and getting that to work but it's kind of neat how that that works out and now we get to actual all proposals so folding practice planning on doing this but it's an explicit comment to that effect so we're going to fold some letters of the alphabet you have in your packet instructions for making the individual digits six four eight and nine and you also have which are all pretty easy you also have a diagram for it's crazy design called typeset which can desync this same folding can make any letter of the alphabet and any digit so just to show you what they will look like these are my foldings of six eight four and nine according to the first set of diagrams and then this is my folding of think the letter the number six rather out of jason coos design so if you wanted to reconfigure it to i guess eight is kind of hard let me do four think okay so four four I've got a fold this guy under fold this here this tab I think goes back here so the advanced origami folders can definitely do in this classic and if they do the Jason coos design but it it takes a little while I think there I've got a four got it a little hard to hold in position but at least in theory it will make any letter all out of one one folding you just have to move all the tabs around so it's kind of neat but it takes at least half an hour so to fold that unless you're really fast so I would recommend pick one of these working groups if you like if you want you can form a group of 4 and make 6 8 4 & 9 follow the diagrams this is an exercise in following diagrams one way or the other only have time to maybe make one digit each but have fun with it and if you have questions raise your hand I can tell you the first step in 6 8 & 9 is to make an 8x8 grid there's a lot of ways to make an 8x8 grid but an easy one is shown here so you take your your sheet you fold the bottom edge to the top edge I think they want to do it white side up again so they're all valleys when you align those edges you'll get a nice bisector then you repeat folding the bottom edge to the middle and once you do that to save a little bit of time you can then fold that new bottom edge to the middle again that will do eights on one side it's a little bit inaccurate because you're folding through two layers but it's a little faster time is of the essence then you do the same thing on the bottom and you'll get ates in one dimension but then you have to fold it in eighths in the other dimension once you have eighths it's like three steps it's really easy four six eight and nine four uses a different approach it's a little more free hand if you want to be more creative try the four you've got to kind of eyeball what looks and feels good for number four so out of curiosity how many people have an 8x8 grid at this point you want to take full so that's the top half of these diagrams to 8x8 grid then it's mostly folding up over individual edges and some corner folds but they're all they're all simple folds in this world so you're folding through I think always all the layers on this this is only folding through one layer but these would always fall into the some layer simple folds category so for example make a six this bottom edge up fold the left three squares over this corner up fold this corner down fold this down this over there's really big six and these numbers are all pretty much proportioned correctly the four you have to be it helps to have a reference model one of the other digits to make it the right height but it'll end up roughly correct anyway it's a little bit narrow and it's designed it's slightly narrower than the six and the nine but otherwise they're nice compatible digits there's a whole alphabet on the website that's linked from this slide so you can go check it out the origami Club so it's kind of fun to think about font design and alphabet design there's actually a lot of origami alphabets out there this is one of the simplest that has digits anyone have questions how many people folded a letter a digit okay so maybe I will you can keep folding but maybe I'll continue on it's gonna be a lot of fun crackling anyone folded this one anyone working on it uh-huh a bunch of people cool well let me know when you finish it's kind of fun it's not that hard I wanted to point at the origami website or gham it is the origami Club at MIT and at the top you see a different alphabet this is a four fold alphabet designed by Jeannine Mosely who's an MIT alum and came to this class two years ago and so that's the reference design in 2002 I'm not sure if it has digits though at least the the diagrams we found for the letters do not also have digits so I think an interesting challenge is to design a for fit for fold digit set to compliment her letter set if you're interested that could be a cool project to work on folding design minimal fold alphabets you could try a three fold alphabet to fold alphabet whatever also on this website are the meeting schedule it's always Sundays sometimes two sometimes three o'clock check it out and there's a convention coming up our very own origami convention on October 27th and Jason ku wanted me to to remind you about that coming up so if you even if you've never done origami before other than today you should check it out it'll be fun lots of different sessions on from simple models to complicated models this is a cool design by Brian Chen another MIT alum it's one square paper folded into the men's at Montes logo but here instead of the oil lamp you've got a little origami crane cool stuff cool so we proceeded on to other questions this is a pretty simple one at the top of the note says folding any shape aka silhouette folding and gift wrapping it has a couple of references so where do those terms come from it's the question and one answer is it's the title of the paper folding flat silhouettes and wrapping polyhedral packages but that's that's not the real answer so this is the two of us and Joe Mitchell it's also that I think the introduction of the term computational origami but those those terms come from earlier references so in that paper there's a sentence classic open question origami mathematics and we don't really know where it came about but it was first formally posed by Bern and Hayes in this soda 96 paper which we'll be talking about in the next lecture lecture three and this is a quote from their paper is every simple polygon when scaled sufficiently small the silhouette of a flat origami the point of saying the word silhouette is that when you fold something like this number six there's a whole bunch of layers and there's a lot of complexity to this folding by saying silhouette we just mean you know collapse all the layers ignore the coloring and just take the outline so the silhouette of this thing is a rectangle and in general that's the sort of the transformation to throw away the complexity of the folding and say I just care about the shape can I get the desired shape there's some other interesting questions here though which haven't been fully addressed how many creases are necessary to fold well actually to that in a later question how thick must the origami be this the strip method can shows that if you start from a rectangle of paper or the number of layers can be very small I think 2 or 3 is enough for all the gadgets that we use probably 3 if you start from a square though we don't know the answer to that question and in practice folding through many layers is tough yeah so that was the silhouette problem and then the gift-wrapping problem and the motivation is you have a weird-shaped gift you want to wrap it with a piece of paper and this is posed to us in a talk by Janaki Amma at a Canadian geometry conference jun akiyama is really cool guy he he has a math or has had for many many years on mathematics TV show in Japan and he's known throughout Japan because everyone in school watches his videos and it covers really interesting mathematics some of the results in this class are actually in his videos as well it's mostly in Japanese so it's a little hard to for most of us to watch but there's some subtitle versions and they're really fun maybe we can have a movie night and watch one of them I get permission so there isn't a great reference for that I mean written some papers about different kinds of wrapping problems but mostly it was this talk that he gave in 1997 which is when I was just starting out in computational geometry that's where the terms come from a lot of words have you ever actually folded a model using this method of zigzagging and folding with this strip any real or sensible or pretty origami models or is it purely for the sake of universality my knee-jerk reaction was no way is is practical this is just for universality and the point of this theorem has always been in my mind to prove that everything is possible but then the challenge is to find good foldings for some notion of good but actually there is a lot of strip or there's there a bunch of examples of strip folding not a lot of different folds and not terribly many gadgets but there's some cool things especially with strip weaving these are just a few examples of woven colored strips you can make fun things like space invaders you can weave together baskets and do wrap your packages and so on so this is a little bit more bar gammak so there were no real folds in there except at the edges of the cube this one is a modular origami it involves a bunch of different folds to get the all the pieces to lock together modular origami means you have a bunch of identical pieces so they kind of weave together through folding and then you can make a nice little crown this is a very classic model you've probably seen it at some point here that the paper is slit and then it's woven so but there is there's some folds down here so not a lot of folding but strips are pretty neat you can definitely use them all sorts of different designs here's some more sculptural design ii models from taking strips of paper this has no glue in its I think there's more strips at the end lock locking this together and this guy Zachary footer ur2 took a bunch of these kinds of units and started weaving them together and make really complicated shapes so you can definitely do cool things with strip folding and another sort of common one around these days is taking gum or candy wrappers and weaving them to get folding them down into little strips and then weaving them together to make handbags and other things become kind of a fashion trend over the last few years so those are things you can do with strips we have used it in one paper that's where the goal is actually to be efficient and use a small piece of paper and not just prove some universality result this is in our paper folding a better checkerboard which we will talk about I think in two lectures if I recall correctly in more detail but this is sort of a baseline this is not the better method just to develop in this paper but it's sort of the starting point which is you take a square so this actually starts with a square you do this pleating and you get this this is with bicolor paper it's dark on one side light on the other you get this strip of squares in color pattern and then you take that strip a huge number of layers in the middle so it's not super practical but it's actually pretty efficient in terms of how big a square you start with too an n-by-n this is obviously not to scale you need more squares here in order to make this thing and then you just sort of snake your path back and forth you could use turn gadgets or here we're just using 45-degree folds and this is pretty close to what was believed to be the best way to fold a checker board and then this paper shows how to do a factor of two better so we'll talk about that later but there are some uses for strip folding this is a little bit theoretical but it's actually pretty competitive against the best end by end checkerboard foldings in the origami world like the one I showed last class so that's practicality of strip folding next questions more about strip folding there are a couple things that are in the lecture notes the handwritten lecture notes but we're not even mentioned in the audio part of the lecture so a few people asked about what what are these things said pseudo-polynomial upper bound pseudopolynomial is a fun term let me tell you a little bit about it that's from the algorithms world but even a lot of alguns people don't know it so let me tell you so maybe first I should tell you about polynomial in general what these terms are about is measuring how fast an algorithm is so the idea is you plot conceptually n this is the problem size so if you wanted to fold an arbitrary polyhedron the one way to think of the problem size is the number of vertices edges and faces just the the total number of things you're given as input and then your output is whatever but n is supposed to be the input problem size and then on the y-axis you want to do you want to plot running time of your algorithm so this is how long it takes to compute the way to fold your square paper into your desired shape and generally this is going to increase and the question is does it increase in a reasonable way or in a crazy way you know that goes exponentially so you want to know how does the running time grow with n polynomial is a sense of good growth and it just means you grow like n to the C where C is some constant so ideally you'd have n or maybe you have N squared or n cubed or n to the fourth all these are considered good running times not quite as good as polynomial is pseudo polynomial and I would conjecture for this problem of folding an arbitrary given polyhedron you cannot achieve a polynomial number of folds let's say so there are two things we could measure here the running time the algorithm we could measure actually three things we can measure the number of folds you make number of operations you do sort of on the paper and a third thing would be scale factor how big a square do I have to start with in order to make desired polygon and pseudopolynomial means n times R to the C what's R R is some geometric parameter geometric ratio in the input and in particular for this problem what makes sense for our is basically the longest length divided by the shortest length this is typically what R refers to this will come up in later lectures as well so for example you take your entire shape you measure the sort of the diameter of the shape the two farthest points that's your longest length shortest length would be maybe you have a triangle something like this in this target poly huge and you want to make this would be your shortest distance this is actually called the minimum feature size in computational geometry or the minimum altitude of any of your triangles okay so that's just some number and you know you can have a triangle just super super narrow and so it's this ratio are could be arbitrarily large even though you only have three vertices three edges one face so N&R are not necessarily comparable so that's why in pseudo polynomial we put them both together and then we raise them to some constant power that's a pseudo polynomial running time so the the the question is being posed here is can you get a pseudo polynomial upper bound and can you get a pseudo polynomial lower bound and it doesn't say for what but it's for all three problems running time number folds scale factor and not all of these are open so in the original paper there's this theorem that says lots of things you know you can fold anything and it says here the folding requires a number of folds polynomial and N and the ratio R so it already claims that there is a pseudo polynomial bound on the number of faults it doesn't say what that pseudo polynomial bound is is it n times R is it n plus R is it n times R squared I would guess one of the first two and times RN plus R so that's the upper bound question maybe we can work on this in a problem session a lower bound question is do you prove that you need some dependents both on N and R which I would guess is pretty easy if you want to take a square and fold it down to a really really skinny triangle I think you need at least our faults roughly and similarly should need a at least n folds so there should be a lower bound of like n plus R but none of these have been written down explicitly so that's what those open questions are then there's another slide 6 which is completely uncovered it's not me if they're questions I should maybe take a brief moment to breathe so the next part of the lecture notes s about seam placement so seam placement it's the following kind of issue when you fold like this number it's a six this is a nine-fold this number nine in addition to seeing the color pattern if you look closely there's also these kinds of seams this white square is not just a white square you can see on the top layer this crease line and here there's a seam here this the seam these are like visible lines of course you have to have seams at the color transitions but there's other seams as well maybe you want to minimize those seams you want to get you want to place the seams in a cool pattern when you fold checker boards there's a such thing as a seamless checker board where every square is a whole square paper there's no visible crease lines on the top layer so this is an extension of the universality result to also get sort of universal seam placement and what what the original paper proves is that you can place the seams as long however you want provided the seam regions the regions between the seams are convex polygons which is almost always the case you look at a typical model you know here this the seam regions are all rectangles and triangles so this could you could you could achieve exactly the same pattern if you wanted it you could also say oh well here's a nice rectangle I'll make that a seam region here's a nice rectangle make that a seam region but you could not make the entire number 9 here a seam region because it's non-convex least you can't do it with this technique we don't know necessarily whether this is possible by some other folding I would guess no but it is possible to make some non convex seam regions for example I could take this page and fold the corner over and now I've got a non-convex seam region here so some non convex seam regions are possible open question is what seam what if I give you a polygon we know every polygon is possible now I give you a polygon and I subdivide it into seam regions which of those are possible not everything is possible I'm pretty sure though I'm not sure we have a proof of that some things like this little heart shape are possible characterized this is another cool possible problem for a problem session questions about that okay so ah I have a little bit about the proof of how this is done if you wanted to just do convex regions so the general approach here for is you we want to visit all of the regions in some order this is called a tour it's pretty easy to just I mean you're allowed to visit regions more than once so you just keep going keep trying to visit some unvisited seem region when you visit a seam region it's a convex polygon so what we're gonna do is make our strip fairly wide actually wide enough to completely cover that seam region then at this moment we'll basically need to turn to do the next one and so there's we know how to sort of change the direction of this strip using a turn gadget then we have to change the width of the strip maybe it needs to be wider maybe it needs to be thinner and then we need to shift the strip one one way or the other so you know if we just end here we turn we might be misaligned so we need to shift it over expand it then do the next one then turn then shift it over then set the right width keep going like that okay that's pretty messy and complicated but you can do it with these two gadgets strip with gadget you take a strip and you can make it anywhere between 1/2 and 100% of its original width so the idea is you start with a really wide strip wide enough to cover all the polygons then you do this gadget and keep shrinking it by half until it's roughly the right size and then when you're almost correct you shrink it by a little bit more here drinking to 1/3 and then you get your shrunken strip and it happens right at the the line that you specify so you can basically on a dime shrink your strip and then by doing the reverse you can grow it back this is maybe not with simple folds though then the other gadget is a shift gadget where you're just you're at this position you want to shift up so that's pretty easy you just do to turn gadget it's okay so that's how at a high level how that making a desired seam pattern works go on to the next question a lot of people asked about this and so this is an open problem that I mentioned orally it's not written in the notes which is can you actually do the things that we said we can do with simple faults so can you get a universal folding of a polygon to color pattern polyhedron using simple faults and I thought it would be fun to actually work on this here live because I think this is an easy problem and there's a bunch of possible answers and there are even two suggested ideas from the comment skill so let me just remind you of the issue what's happening and then I need your input what's gonna work here so general picture for strip method was we do one triangle we end here then we do a bunch of folds like this and then we and here maybe and then we sig zag and the trouble is we've already made this triangle over here when we make this triangle we have this excess stuff which I haven't drawn very accurately but you recall it looks something like that or maybe even more like that if we use right angle turn gadgets and then we want to fold it underneath and we're doing that the way I said with hi gadget Mountain folds but the model of simple Falls which I should make may be more explicit you're not allowed to collide during the motion it's the idea with the simple fold is that you should be folding along one line segment and you should fold by the model that we defined back in the day I'll I'll talk more about where this notion comes from you fold by plus or minus 180 degrees which means after you do the fold you'll be flat again and no collision during the motion so if we folded this triangle and then we folded this one and this stuff is on the top we can't mountain fold that's not considered a simple fold now one proposal is could we just make the next triangle underneath the previous one a different proposal is Valley fold these are actually different proposals because especially for two color patterns it'll make a difference if we weave Valley fold here there's gonna be some junk on the front side especially if you want to get a desired seam pattern but maybe we'll leave seam patterns for later if you want to get a color pattern you might reveal some wrong color when you do that Valley fold so I haven't really thought about this idea yet I think it might be good so the idea there would be so you've already made this triangle you've out you Mountain fold everything now when you go when you do these zigzags you want to be underneath everything that you've done yeah okay different idea as you basically fold this out of the way do this thing hide gadget and then fold it back maybe I've wondered about that too it's it's gonna get a little challenging them in general there's a huge set of triangles so unless you can like go far away make your triangle and then plop it down maybe it's possible ah I guess we can pursue that idea but maybe first we should exhaust the easier ideas so I mean that is definitely plausible that's possible doing that with simple folds and not leaving any garbage is gonna be a little challenging but might be doable this to me is the simplest idea so we should first see if it works anyone see problems with this plan so guess we should think about I have some strips we could think about what it means to be doing a turn gadget underneath here so I don't know quite about well let's suppose we're already here and now maybe I do some as a turn gadget goat some mountain folds then a at 90 degrees and then a valley fold like that and then I do a mountain fold I think it might be okay because turn gadgets start with a mountain fold which so if you're underneath everything that's gonna avoid collision and then the valley fold is brings it back with again we're using just the space below everything that we see so then we make that strip we keep turning around and then later on we're going to mount and fold this behind somehow to meet this edge no seams okay yeah question yeah going from one triangle to next yeah so we could think about that too it's it's very you're right I mean I'm just looking at the turning-around part for making a single triangle but there's also the turn gadget going from here to here it's actually slightly more complicated that we've covered in class but not really much it's just a slightly generalized trend gadget so you're coming here you basically want to turn around so but let's just think about a way to do it you could imagine first doing a turn like this it's not exactly a pure turn gadget and then turning around to get to the next place this is really hard to do on a blackboard strips just tend not to stay together very well okay now we're going parallel to the correct direction then we turn back and forth but each of those is just using turn gadgets so as long as the turn gadget works fine a turn gadget is gonna be a mountain fold we're just gonna go behind everything and then a valley fold to bring it to a desired direction those are all using everything behind the board so it seems like all those operations are okay now we should also check the color reversal gadget which it's funny thing I remember everything I did before 2000 or so so I still have memorized the color reversal gauge at least I think so I should probably color this piece of paper so you can see the colors change I don't remember anything I've done since 2000 but anything up to 2000 I'm okay this is 1998 I think I remember falling Lots this is ticker tape they use for or not ticker tape but just use this for like adding machines so I think it's a 90 degree mountain fold then you fold up like that and then you fold back down with a mountain fold like that and you get a color reversal on all of those folds were working behind my plane here so should avoid collision with everything I think you can do color reversal and turn gadgets behind and so this suggestion works who made this suggestion good idea so unless there any objections I think that will work I had a different plan which was to use this second idea and set up the turn gadget so there was no when you fold this with a valley fold there's no ugly colors so you could maybe modify the turn gadget to be completely solidly colored on both sides but I think this is much easier it's probably why I didn't write it down the notes but I'm not sure yeah go far away make a triangle okay how do you do that last part what's so I mean you have to do it with simple folds that's the main that's the challenge so the idea is you you're way out here you have a triangle out here which you want to bring over here maybe I should do it like this so you could do something like this so now the triangles over here then maybe you want to go most all the way here and then fold it back and then fold it forth and back until you get your triangle exactly where you want it it seems possible my only concern would be when you do this thing there might be a little little corner depends how you fold this thing and then you've got to hide that corner and if there's triangles all around here there may not be room I mean maybe there's triangles all around here it's okay to have that corner but maybe the triangles are different colors so I I do believe that should be possible it's but I think it is a little bit more complicated because you have to hide one last piece after you get it in position anyway I think there are at least three ways to solve this problem yeah are you allowed to unfold it's a good question I don't remember whether the original model says whether you're allowed to unfold so there are two versions simple folds and unfolds or just simple folds I don't think we actually said unfolding is allowed so we're definitely thinking about at some point it's probably not in the model as defined there questions all right what's next this is the paper that introduced simple folds it's called when can you fold a map because it originally was motivated by a map folding and it had a bunch of reasons for introducing simple folds among them here's this quote which if you've watched l1 as in there I think the easiest way to refold a road map is differently coalesce to make it easier to refold your road map correctly but here's one quote from that paper as motivation so is origami motivation but we're also wondering about applications like sheet metal bending cardboard folding things like that where you want to manufacture things using a machine and while origamist can do complicated folds non simple folds to make artwork practical manufacturing you want to have the simplest possible machine so if you can get away with just simple folds as defined here that would be great now you don't really need some of these are maybe artificial you probably don't need the 180 degree condition because most of the things you want to fold aren't flat we introduced that just to keep things simple mathematically but you'd like to fold along just one segment at a time ideally you definitely don't want collision so you don't want the material to hit things whereas in origami you can do tuck so you can do things that you know are not simple folds it's a lot harder with a machine that doesn't have any feedback so here's a very simple machine this is a a break folder we actually have a break folder in CC although this one is electro break so this has an electric assist so the idea is you slide your sheet in and you hold here you pull up and in this case is bending to a 90 degree angle but you can adjust it to different angles and so on so that and there are lots of automated machines a little hard to get photos and videos of them but they're based on this principle maybe you you push in a V and you end up with a crease in one spot and you'd like to just make sort of conveyor belt with lots of different pushes and pulls and do a bunch of simple folds basically except for this 180-degree constraint and so we're just curious about what's possible by simple folds and that led us into the mat folding stuff where it's fairly easy to characterize other things where it's harder which we'll see in lecture 3 I thought I'd show you some examples of things people make with pretty much simple folds other than this 180 condition out of things like this is folding wood so you take sheet material and you start bending these parts up and you can make a little chair a little table and you can fold it back when you're not using your living room you can hide everything so you could imagine also having multiple sheets and sometimes your room is a living room other times it's a whatever furniture you need you just unfold the appropriate thing it's kind of a vision here's a cute little folding card there's a huge number of folding chairs but this one is pretty much simple folds the one thing I'm not sure where there falls under simple fold is this fold so it's you do fold along one line but it's in two different pieces not sure we'd call that a simple fold there's of course lots of slits in the material here but of course it has all the same advantages of simple folds this is easy to execute one step at a time here's some more complicated designs some of these are computer rendering some of these are real again too taking furniture out of flat walls here's some table designs these are of sheet metal I like I like this one it's very simple take a square of sheet metal put in some slits do some very simple folds boom you've got a table this one's also pretty simple here we again here we're folding along one line but it's in two different pieces so is that a simple fold is definitely harder to build such a machine but it's doable here we have something's definitely not a simple fold but it's also fairly easy to execute using our roller you can kind of curve one segment so I mean when you go to reality there's you can change the model in all sorts of different ways and still have something practical and no one rule set is is gospel but mathematically we have to hone in on at least one model at a time and then we can see how changing the rules changes what you can make okay next question this is actually about the definition of simple folds so it's probably answered already is allowed to bend the rest of paper to get it out of the way avoid collision the answer is no in simple folds at least you're you're only allowed to move that one segment we have actually lately been thinking about a different model where you do allow this but simple folds you can't move other parts you can just move the single hinge that you're folding and the end product has to be flat yes in our model though it'd be interesting to think without this condition because you're doing 180 degree operations before you do the next one you will be flat at all times 1d or 2d according to whether you started with a 1d piece of paper or a 2d piece of paper okay so in then the second half of the lecture was basically about proving characterizing flat foldability of 1d segments and it showed in particular that simple folds are universal that you if you have some Mountain Valley pattern and it's foldable at all if it's flat foldable it will be flat foldable via simple folds and in particular using crimps and n folds so let me and there and it was a bit of a messy proof partly because I've made a mistake in lecture as you saw I kind of corrected for it on the fly but it's maybe not the best written so I wanted to go through a couple quick examples to make clear all the issues there so here are the ones I prepared we can certainly do more if it's still not clear so here's a simple Mountain Valley pattern and it's got some long segments and let's just say equidistant segments here 3 valleys than a mountain so first question is is this mingling and then this the ultimate question is is it flat foldable so is it mingling well maybe you can answer for me just yes or no 50% chance okay so maybe the definition of mingling is not super clear let me review it so you look at each I mean generally of a sequence of mountains and valleys so you look at a chunk of all valleys then you look at a chunk of all mountains and chunk of all valleys here there's only two chunks three valleys and one mountain and the definition is a little awkward for a single crease but let's start with the all valleys the point is to check for the first segment between two valleys versus the segments just before it which is bigger and this is the bad case this is the non mingling situation because this thing is bigger than this strictly bigger it's strictly bigger the notation we used and the lecture is an open square bracket so square bracket meant that this is bigger round bracket would mean this is less than or equal to this that's just the definition over on this side of the valleys this length is equal to this length so the last distance between two valleys is equal to the one right after it and so that's a good case so we write a closed round bracket then we have a sequence of mountains and here it's a little confusing but it's the same idea you look at so this is the very first mountain you look at the length right after it versus the length right before it and this is smaller and so that's a good case we write an open round bracket for this mountain group and then same thing now we're comparing the same two distances but it's now bad because this one is strictly longer than this one so we write a closed square bracket so that's the notation in this example any questions about that so you just have to check we're looking in general you have a whole group of valleys because these are all valleys or all mountains and you want to compare this one versus this one and it's square closed according to which is bigger and you want to look at the last one versus the after last one okay so that's the notation and the point of the proof was to argue that either there's a if you're gonna be flat foldable at all actually if you're mingling mingling meant that for each of these intervals at least one of the sides was round that was considered good so this crease pattern is mingling because there's two regions this one has a round bracket this one has a round bracket and what we argued is that if you're mingling you which was necessary if you're flat foldable you have to be mingling it's a necessary of a not sufficient condition for flat foldability if you're mingling either you have a pattern like this close round bracket open round bracket that's good because this is a crimp that you can do and you can see it up here this is a crimp you Valley fold mountain fold and you don't hide anything when you make that operation or there's an end fold which correspond it to an open round bracket at the beginning or a closed round bracket at the end so here there's a crimp let's do the crimp so when we do the crimp let's keep this part of the paper fixed so this we go over to here roughly then we valley fold then we mountain fold and we keep going from there it's that segment is that signal okay so we still have this this valley this was the valley we just folded this is the mountain we just folded now conceptually we just sort of fuse this back into the paper because those creases are done we don't need to think about them the point is in that region there were no extra creases this these round parentheses will guarantee there's nothing here no creases here here or here could be creases farther away but you buy these inequalities that this length is less or equal to this one and this length is less or equal to this one let's try greater than or equal to equal to then you know this is okay okay crimp so there's two valleys left so now we have two valleys we have a long segment in a long segment and this is something that can't be made because if you I mean there's no folded state of this thing never mind simple folds because it's gonna cross like that so this is not flat foldable yeah it's also not mingling because if you look at these two valleys you look at the distance over here that's bigger than this one so that's bad so you have an open square bracket and this one is also bigger than this imagining these is fused and so it's a closed square bracket and so this group of valleys is not mingling so it's not mingling so ultimately this pattern we started with is not flat foldable because one of the things we proved is that doing a crimp never changes flat foldability it's always a safe thing to do so I mean there was I mean you might wonder oh maybe there's some other fold I could do that eventually works but we proved crimps are always safe to do so and we did it and we got stuck that means this was not flat foldable even though it was mingling and so the mingling forever property just means if it's mingling and when you do a crimp and is still mingling and if you keep doing crimson it stays mingling all the way then you were flat foldable it's not a very satisfying characterization but it is a thing maybe I'll do one more example just to where it works we're super clear Oh out of time so I won't do another example all right ambitious yeah and I got to work on my timing there are a couple other fun questions here I would encourage you to read the notes about them in particular there's an algorithmic question how do you actually compute this efficiently you can do it very efficiently in linear time so and where C is one just n time instead of N squared or something using a pretty simple idea basically just look for the first crimp to do it and then see if they're crimps nearby and keep going forward and you can prove that takes linear time there is this fun question I enjoyed thinking about can you make any Mountain Valley pattern flat foldable by adding creases the answer is yes I can think of it as a puzzle there's one proposed way to do it here I have another one in the notes you can think about it and the last question is what is it possibly mean to fold something in four dimensions how do you imagine it hard to imagine but you can think about it you have a d-dimensional piece of paper you fold it through D plus one dimensions if you want to flat fold it it ends up back in D dimensions and your creases are D minus one dimensional and the rest you just have to visualize I have one example of folding a solid cube in half in the notes that's certainly possible it's not very well studied and there's lots of interesting open questions about higher dimensional folding any questions before we go all right watch lecture three and please send your feedback is really helpful you 3 00:00:07,990 --> 00:00:11,650 4 00:00:11,650 --> 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--> 00:15:58,900 330 00:15:58,900 --> 00:16:00,790 331 00:16:00,790 --> 00:16:04,720 332 00:16:04,720 --> 00:16:07,600 333 00:16:07,600 --> 00:16:10,990 334 00:16:10,990 --> 00:16:12,280 335 00:16:12,280 --> 00:16:13,509 336 00:16:13,509 --> 00:16:16,329 337 00:16:16,329 --> 00:16:18,160 338 00:16:18,160 --> 00:16:21,540 339 00:16:21,540 --> 00:16:24,460 340 00:16:24,460 --> 00:16:26,769 341 00:16:26,769 --> 00:16:28,660 342 00:16:28,660 --> 00:16:32,350 343 00:16:32,350 --> 00:16:34,930 344 00:16:34,930 --> 00:16:36,100 345 00:16:36,100 --> 00:16:37,889 346 00:16:37,889 --> 00:16:40,420 347 00:16:40,420 --> 00:16:43,360 348 00:16:43,360 --> 00:16:44,980 349 00:16:44,980 --> 00:16:46,929 350 00:16:46,929 --> 00:16:48,189 351 00:16:48,189 --> 00:16:50,949 352 00:16:50,949 --> 00:16:52,629 353 00:16:52,629 --> 00:16:55,389 354 00:16:55,389 --> 00:16:57,189 355 00:16:57,189 --> 00:16:59,050 356 00:16:59,050 --> 00:17:01,629 357 00:17:01,629 --> 00:17:03,610 358 00:17:03,610 --> 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388 00:18:10,799 --> 00:18:13,590 389 00:18:13,590 --> 00:18:15,900 390 00:18:15,900 --> 00:18:21,900 391 00:18:21,900 --> 00:18:24,780 392 00:18:24,780 --> 00:18:27,570 393 00:18:27,570 --> 00:18:31,020 394 00:18:31,020 --> 00:18:35,010 395 00:18:35,010 --> 00:18:44,700 396 00:18:44,700 --> 00:18:47,659 397 00:18:47,659 --> 00:18:49,799 398 00:18:49,799 --> 00:18:51,210 399 00:18:51,210 --> 00:18:53,220 400 00:18:53,220 --> 00:18:55,289 401 00:18:55,289 --> 00:18:56,880 402 00:18:56,880 --> 00:18:58,470 403 00:18:58,470 --> 00:19:01,169 404 00:19:01,169 --> 00:19:04,770 405 00:19:04,770 --> 00:19:06,990 406 00:19:06,990 --> 00:19:10,320 407 00:19:10,320 --> 00:19:11,970 408 00:19:11,970 --> 00:19:14,070 409 00:19:14,070 --> 00:19:17,130 410 00:19:17,130 --> 00:19:19,560 411 00:19:19,560 --> 00:19:21,850 412 00:19:21,850 --> 00:19:23,740 413 00:19:23,740 --> 00:19:26,529 414 00:19:26,529 --> 00:19:28,810 415 00:19:28,810 --> 00:19:32,169 416 00:19:32,169 --> 00:19:39,549 417 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--> 00:21:18,549 447 00:21:18,549 --> 00:21:20,110 448 00:21:20,110 --> 00:21:23,139 449 00:21:23,139 --> 00:21:24,460 450 00:21:24,460 --> 00:21:25,990 451 00:21:25,990 --> 00:21:28,840 452 00:21:28,840 --> 00:21:31,690 453 00:21:31,690 --> 00:21:34,060 454 00:21:34,060 --> 00:21:35,440 455 00:21:35,440 --> 00:21:38,769 456 00:21:38,769 --> 00:21:40,659 457 00:21:40,659 --> 00:21:42,129 458 00:21:42,129 --> 00:21:45,460 459 00:21:45,460 --> 00:21:47,440 460 00:21:47,440 --> 00:21:48,789 461 00:21:48,789 --> 00:21:51,009 462 00:21:51,009 --> 00:21:52,870 463 00:21:52,870 --> 00:21:56,620 464 00:21:56,620 --> 00:22:00,190 465 00:22:00,190 --> 00:22:01,299 466 00:22:01,299 --> 00:22:02,860 467 00:22:02,860 --> 00:22:04,629 468 00:22:04,629 --> 00:22:06,279 469 00:22:06,279 --> 00:22:09,700 470 00:22:09,700 --> 00:22:13,570 471 00:22:13,570 --> 00:22:16,600 472 00:22:16,600 --> 00:22:18,310 473 00:22:18,310 --> 00:22:20,139 474 00:22:20,139 --> 00:22:21,730 475 00:22:21,730 --> 00:22:26,639 476 00:22:26,639 --> 00:22:29,710 477 00:22:29,710 --> 00:22:31,539 478 00:22:31,539 --> 00:22:33,759 479 00:22:33,759 --> 00:22:37,029 480 00:22:37,029 --> 00:22:40,419 481 00:22:40,419 --> 00:22:43,360 482 00:22:43,360 --> 00:22:46,269 483 00:22:46,269 --> 00:22:48,009 484 00:22:48,009 --> 00:22:49,990 485 00:22:49,990 --> 00:22:52,899 486 00:22:52,899 --> 00:22:55,120 487 00:22:55,120 --> 00:22:57,220 488 00:22:57,220 --> 00:22:59,019 489 00:22:59,019 --> 00:23:00,909 490 00:23:00,909 --> 00:23:04,600 491 00:23:04,600 --> 00:23:06,700 492 00:23:06,700 --> 00:23:08,169 493 00:23:08,169 --> 00:23:11,139 494 00:23:11,139 --> 00:23:12,610 495 00:23:12,610 --> 00:23:15,009 496 00:23:15,009 --> 00:23:16,930 497 00:23:16,930 --> 00:23:19,269 498 00:23:19,269 --> 00:23:21,250 499 00:23:21,250 --> 00:23:26,139 500 00:23:26,139 --> 00:23:28,799 501 00:23:28,799 --> 00:23:31,810 502 00:23:31,810 --> 00:23:34,210 503 00:23:34,210 --> 00:23:39,190 504 00:23:39,190 --> 00:23:41,259 505 00:23:41,259 --> 00:23:43,240 506 00:23:43,240 --> 00:23:45,269 507 00:23:45,269 --> 00:23:48,369 508 00:23:48,369 --> 00:23:49,180 509 00:23:49,180 --> 00:23:53,050 510 00:23:53,050 --> 00:23:55,120 511 00:23:55,120 --> 00:23:58,720 512 00:23:58,720 --> 00:24:00,280 513 00:24:00,280 --> 00:24:03,280 514 00:24:03,280 --> 00:24:05,140 515 00:24:05,140 --> 00:24:07,000 516 00:24:07,000 --> 00:24:11,470 517 00:24:11,470 --> 00:24:13,000 518 00:24:13,000 --> 00:24:14,950 519 00:24:14,950 --> 00:24:16,960 520 00:24:16,960 --> 00:24:19,680 521 00:24:19,680 --> 00:24:22,750 522 00:24:22,750 --> 00:24:24,760 523 00:24:24,760 --> 00:24:28,540 524 00:24:28,540 --> 00:24:30,580 525 00:24:30,580 --> 00:24:33,430 526 00:24:33,430 --> 00:24:35,680 527 00:24:35,680 --> 00:24:37,690 528 00:24:37,690 --> 00:24:40,870 529 00:24:40,870 --> 00:24:43,990 530 00:24:43,990 --> 00:24:45,730 531 00:24:45,730 --> 00:24:48,970 532 00:24:48,970 --> 00:24:51,160 533 00:24:51,160 --> 00:24:52,990 534 00:24:52,990 --> 00:24:54,850 535 00:24:54,850 --> 00:24:56,770 536 00:24:56,770 --> 00:24:58,780 537 00:24:58,780 --> 00:25:01,060 538 00:25:01,060 --> 00:25:05,140 539 00:25:05,140 --> 00:25:06,760 540 00:25:06,760 --> 00:25:09,520 541 00:25:09,520 --> 00:25:11,770 542 00:25:11,770 --> 00:25:15,220 543 00:25:15,220 --> 00:25:19,390 544 00:25:19,390 --> 00:25:21,190 545 00:25:21,190 --> 00:25:26,590 546 00:25:26,590 --> 00:25:29,160 547 00:25:29,160 --> 00:25:31,600 548 00:25:31,600 --> 00:25:35,350 549 00:25:35,350 --> 00:25:38,560 550 00:25:38,560 --> 00:25:40,390 551 00:25:40,390 --> 00:25:42,130 552 00:25:42,130 --> 00:25:44,320 553 00:25:44,320 --> 00:25:46,120 554 00:25:46,120 --> 00:25:48,040 555 00:25:48,040 --> 00:25:50,890 556 00:25:50,890 --> 00:25:54,130 557 00:25:54,130 --> 00:25:56,260 558 00:25:56,260 --> 00:25:58,669 559 00:25:58,669 --> 00:26:02,910 560 00:26:02,910 --> 00:26:06,330 561 00:26:06,330 --> 00:26:08,460 562 00:26:08,460 --> 00:26:11,940 563 00:26:11,940 --> 00:26:15,780 564 00:26:15,780 --> 00:26:17,910 565 00:26:17,910 --> 00:26:21,240 566 00:26:21,240 --> 00:26:22,650 567 00:26:22,650 --> 00:26:24,330 568 00:26:24,330 --> 00:26:26,610 569 00:26:26,610 --> 00:26:29,520 570 00:26:29,520 --> 00:26:31,440 571 00:26:31,440 --> 00:26:33,270 572 00:26:33,270 --> 00:26:35,400 573 00:26:35,400 --> 00:26:39,600 574 00:26:39,600 --> 00:26:41,400 575 00:26:41,400 --> 00:26:43,980 576 00:26:43,980 --> 00:26:45,870 577 00:26:45,870 --> 00:26:48,780 578 00:26:48,780 --> 00:26:52,200 579 00:26:52,200 --> 00:26:53,790 580 00:26:53,790 --> 00:26:56,760 581 00:26:56,760 --> 00:27:00,450 582 00:27:00,450 --> 00:27:02,880 583 00:27:02,880 --> 00:27:05,880 584 00:27:05,880 --> 00:27:08,190 585 00:27:08,190 --> 00:27:11,040 586 00:27:11,040 --> 00:27:14,190 587 00:27:14,190 --> 00:27:18,600 588 00:27:18,600 --> 00:27:20,040 589 00:27:20,040 --> 00:27:23,280 590 00:27:23,280 --> 00:27:25,169 591 00:27:25,169 --> 00:27:29,520 592 00:27:29,520 --> 00:27:31,740 593 00:27:31,740 --> 00:27:33,510 594 00:27:33,510 --> 00:27:36,000 595 00:27:36,000 --> 00:27:38,250 596 00:27:38,250 --> 00:27:40,470 597 00:27:40,470 --> 00:27:42,360 598 00:27:42,360 --> 00:27:46,049 599 00:27:46,049 --> 00:27:48,720 600 00:27:48,720 --> 00:27:50,940 601 00:27:50,940 --> 00:27:53,100 602 00:27:53,100 --> 00:27:56,190 603 00:27:56,190 --> 00:27:59,840 604 00:27:59,840 --> 00:28:03,450 605 00:28:03,450 --> 00:28:05,400 606 00:28:05,400 --> 00:28:07,230 607 00:28:07,230 --> 00:28:09,750 608 00:28:09,750 --> 00:28:11,139 609 00:28:11,139 --> 00:28:15,190 610 00:28:15,190 --> 00:28:18,399 611 00:28:18,399 --> 00:28:23,739 612 00:28:23,739 --> 00:28:27,159 613 00:28:27,159 --> 00:28:28,930 614 00:28:28,930 --> 00:28:30,719 615 00:28:30,719 --> 00:28:34,239 616 00:28:34,239 --> 00:28:35,829 617 00:28:35,829 --> 00:28:39,729 618 00:28:39,729 --> 00:28:41,680 619 00:28:41,680 --> 00:28:46,419 620 00:28:46,419 --> 00:28:47,979 621 00:28:47,979 --> 00:28:52,629 622 00:28:52,629 --> 00:28:54,249 623 00:28:54,249 --> 00:28:55,509 624 00:28:55,509 --> 00:28:57,849 625 00:28:57,849 --> 00:29:00,820 626 00:29:00,820 --> 00:29:03,909 627 00:29:03,909 --> 00:29:07,229 628 00:29:07,229 --> 00:29:10,539 629 00:29:10,539 --> 00:29:14,229 630 00:29:14,229 --> 00:29:17,709 631 00:29:17,709 --> 00:29:21,099 632 00:29:21,099 --> 00:29:22,839 633 00:29:22,839 --> 00:29:25,119 634 00:29:25,119 --> 00:29:28,269 635 00:29:28,269 --> 00:29:29,799 636 00:29:29,799 --> 00:29:32,999 637 00:29:32,999 --> 00:29:35,259 638 00:29:35,259 --> 00:29:38,109 639 00:29:38,109 --> 00:29:40,239 640 00:29:40,239 --> 00:29:42,609 641 00:29:42,609 --> 00:29:46,719 642 00:29:46,719 --> 00:29:48,369 643 00:29:48,369 --> 00:29:55,450 644 00:29:55,450 --> 00:29:56,739 645 00:29:56,739 --> 00:29:58,989 646 00:29:58,989 --> 00:30:02,909 647 00:30:02,909 --> 00:30:11,739 648 00:30:11,739 --> 00:30:14,259 649 00:30:14,259 --> 00:30:16,180 650 00:30:16,180 --> 00:30:19,719 651 00:30:19,719 --> 00:30:22,340 652 00:30:22,340 --> 00:30:24,200 653 00:30:24,200 --> 00:30:29,210 654 00:30:29,210 --> 00:30:37,999 655 00:30:37,999 --> 00:30:39,289 656 00:30:39,289 --> 00:30:41,600 657 00:30:41,600 --> 00:30:44,019 658 00:30:44,019 --> 00:30:48,529 659 00:30:48,529 --> 00:30:51,259 660 00:30:51,259 --> 00:30:54,529 661 00:30:54,529 --> 00:30:56,720 662 00:30:56,720 --> 00:30:59,180 663 00:30:59,180 --> 00:31:00,879 664 00:31:00,879 --> 00:31:04,879 665 00:31:04,879 --> 00:31:06,980 666 00:31:06,980 --> 00:31:08,990 667 00:31:08,990 --> 00:31:10,369 668 00:31:10,369 --> 00:31:12,350 669 00:31:12,350 --> 00:31:13,730 670 00:31:13,730 --> 00:31:16,779 671 00:31:16,779 --> 00:31:18,980 672 00:31:18,980 --> 00:31:26,090 673 00:31:26,090 --> 00:31:30,830 674 00:31:30,830 --> 00:31:34,190 675 00:31:34,190 --> 00:31:36,499 676 00:31:36,499 --> 00:31:39,289 677 00:31:39,289 --> 00:31:40,840 678 00:31:40,840 --> 00:31:52,549 679 00:31:52,549 --> 00:31:55,009 680 00:31:55,009 --> 00:31:57,320 681 00:31:57,320 --> 00:32:00,919 682 00:32:00,919 --> 00:32:02,629 683 00:32:02,629 --> 00:32:04,430 684 00:32:04,430 --> 00:32:06,889 685 00:32:06,889 --> 00:32:09,499 686 00:32:09,499 --> 00:32:14,960 687 00:32:14,960 --> 00:32:16,789 688 00:32:16,789 --> 00:32:19,100 689 00:32:19,100 --> 00:32:21,230 690 00:32:21,230 --> 00:32:22,700 691 00:32:22,700 --> 00:32:25,759 692 00:32:25,759 --> 00:32:28,570 693 00:32:28,570 --> 00:32:31,190 694 00:32:31,190 --> 00:32:32,960 695 00:32:32,960 --> 00:32:35,350 696 00:32:35,350 --> 00:32:37,539 697 00:32:37,539 --> 00:32:40,960 698 00:32:40,960 --> 00:32:45,010 699 00:32:45,010 --> 00:32:48,430 700 00:32:48,430 --> 00:32:51,220 701 00:32:51,220 --> 00:32:51,230 702 00:32:51,230 --> 00:32:51,700 703 00:32:51,700 --> 00:32:56,140 704 00:32:56,140 --> 00:33:01,570 705 00:33:01,570 --> 00:33:04,799 706 00:33:04,799 --> 00:33:08,470 707 00:33:08,470 --> 00:33:11,049 708 00:33:11,049 --> 00:33:14,140 709 00:33:14,140 --> 00:33:16,960 710 00:33:16,960 --> 00:33:19,150 711 00:33:19,150 --> 00:33:22,090 712 00:33:22,090 --> 00:33:24,310 713 00:33:24,310 --> 00:33:27,640 714 00:33:27,640 --> 00:33:29,620 715 00:33:29,620 --> 00:33:32,169 716 00:33:32,169 --> 00:33:38,789 717 00:33:38,789 --> 00:33:43,049 718 00:33:43,049 --> 00:34:00,510 719 00:34:00,510 --> 00:34:03,210 720 00:34:03,210 --> 00:34:05,830 721 00:34:05,830 --> 00:34:07,470 722 00:34:07,470 --> 00:34:09,790 723 00:34:09,790 --> 00:34:11,320 724 00:34:11,320 --> 00:34:13,510 725 00:34:13,510 --> 00:34:14,710 726 00:34:14,710 --> 00:34:16,659 727 00:34:16,659 --> 00:34:18,669 728 00:34:18,669 --> 00:34:20,889 729 00:34:20,889 --> 00:34:25,810 730 00:34:25,810 --> 00:34:28,810 731 00:34:28,810 --> 00:34:36,379 732 00:34:36,379 --> 00:34:39,270 733 00:34:39,270 --> 00:34:44,010 734 00:34:44,010 --> 00:34:47,220 735 00:34:47,220 --> 00:34:51,450 736 00:34:51,450 --> 00:34:52,470 737 00:34:52,470 --> 00:34:54,300 738 00:34:54,300 --> 00:34:56,190 739 00:34:56,190 --> 00:34:58,920 740 00:34:58,920 --> 00:35:00,390 741 00:35:00,390 --> 00:35:03,240 742 00:35:03,240 --> 00:35:05,100 743 00:35:05,100 --> 00:35:07,770 744 00:35:07,770 --> 00:35:11,850 745 00:35:11,850 --> 00:35:14,250 746 00:35:14,250 --> 00:35:15,750 747 00:35:15,750 --> 00:35:17,940 748 00:35:17,940 --> 00:35:20,030 749 00:35:20,030 --> 00:35:22,380 750 00:35:22,380 --> 00:35:26,700 751 00:35:26,700 --> 00:35:29,040 752 00:35:29,040 --> 00:35:29,820 753 00:35:29,820 --> 00:35:32,310 754 00:35:32,310 --> 00:35:35,370 755 00:35:35,370 --> 00:35:36,900 756 00:35:36,900 --> 00:35:40,770 757 00:35:40,770 --> 00:35:46,140 758 00:35:46,140 --> 00:35:48,720 759 00:35:48,720 --> 00:35:50,250 760 00:35:50,250 --> 00:35:52,740 761 00:35:52,740 --> 00:35:55,160 762 00:35:55,160 --> 00:35:58,860 763 00:35:58,860 --> 00:36:00,780 764 00:36:00,780 --> 00:36:02,190 765 00:36:02,190 --> 00:36:07,230 766 00:36:07,230 --> 00:36:09,120 767 00:36:09,120 --> 00:36:10,470 768 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--> 00:37:48,910 798 00:37:48,910 --> 00:37:50,530 799 00:37:50,530 --> 00:37:53,230 800 00:37:53,230 --> 00:37:55,630 801 00:37:55,630 --> 00:37:56,890 802 00:37:56,890 --> 00:37:59,170 803 00:37:59,170 --> 00:38:02,170 804 00:38:02,170 --> 00:38:04,390 805 00:38:04,390 --> 00:38:05,560 806 00:38:05,560 --> 00:38:07,870 807 00:38:07,870 --> 00:38:11,380 808 00:38:11,380 --> 00:38:12,700 809 00:38:12,700 --> 00:38:13,390 810 00:38:13,390 --> 00:38:17,380 811 00:38:17,380 --> 00:38:19,300 812 00:38:19,300 --> 00:38:22,480 813 00:38:22,480 --> 00:38:24,430 814 00:38:24,430 --> 00:38:27,160 815 00:38:27,160 --> 00:38:30,460 816 00:38:30,460 --> 00:38:33,400 817 00:38:33,400 --> 00:38:35,290 818 00:38:35,290 --> 00:38:36,820 819 00:38:36,820 --> 00:38:42,550 820 00:38:42,550 --> 00:38:45,760 821 00:38:45,760 --> 00:38:47,230 822 00:38:47,230 --> 00:38:49,089 823 00:38:49,089 --> 00:38:52,660 824 00:38:52,660 --> 00:38:56,589 825 00:38:56,589 --> 00:38:56,599 826 00:38:56,599 --> 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856 00:39:57,710 --> 00:39:58,880 857 00:39:58,880 --> 00:40:00,590 858 00:40:00,590 --> 00:40:03,560 859 00:40:03,560 --> 00:40:07,070 860 00:40:07,070 --> 00:40:09,230 861 00:40:09,230 --> 00:40:12,880 862 00:40:12,880 --> 00:40:19,370 863 00:40:19,370 --> 00:40:21,290 864 00:40:21,290 --> 00:40:24,020 865 00:40:24,020 --> 00:40:26,510 866 00:40:26,510 --> 00:40:30,770 867 00:40:30,770 --> 00:40:33,350 868 00:40:33,350 --> 00:40:35,050 869 00:40:35,050 --> 00:40:38,300 870 00:40:38,300 --> 00:40:40,490 871 00:40:40,490 --> 00:40:42,140 872 00:40:42,140 --> 00:40:45,080 873 00:40:45,080 --> 00:40:48,290 874 00:40:48,290 --> 00:40:50,030 875 00:40:50,030 --> 00:40:51,950 876 00:40:51,950 --> 00:40:54,260 877 00:40:54,260 --> 00:40:56,290 878 00:40:56,290 --> 00:40:59,030 879 00:40:59,030 --> 00:41:00,650 880 00:41:00,650 --> 00:41:02,450 881 00:41:02,450 --> 00:41:04,490 882 00:41:04,490 --> 00:41:06,740 883 00:41:06,740 --> 00:41:07,850 884 00:41:07,850 --> 00:41:09,479 885 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--> 00:42:19,259 915 00:42:19,259 --> 00:42:21,640 916 00:42:21,640 --> 00:42:24,880 917 00:42:24,880 --> 00:42:27,009 918 00:42:27,009 --> 00:42:29,319 919 00:42:29,319 --> 00:42:32,559 920 00:42:32,559 --> 00:42:37,209 921 00:42:37,209 --> 00:42:39,430 922 00:42:39,430 --> 00:42:41,319 923 00:42:41,319 --> 00:42:42,609 924 00:42:42,609 --> 00:42:45,219 925 00:42:45,219 --> 00:42:47,229 926 00:42:47,229 --> 00:42:49,120 927 00:42:49,120 --> 00:42:52,599 928 00:42:52,599 --> 00:42:54,969 929 00:42:54,969 --> 00:42:56,829 930 00:42:56,829 --> 00:42:58,120 931 00:42:58,120 --> 00:43:00,339 932 00:43:00,339 --> 00:43:05,380 933 00:43:05,380 --> 00:43:07,329 934 00:43:07,329 --> 00:43:09,130 935 00:43:09,130 --> 00:43:12,849 936 00:43:12,849 --> 00:43:15,069 937 00:43:15,069 --> 00:43:17,440 938 00:43:17,440 --> 00:43:21,009 939 00:43:21,009 --> 00:43:22,450 940 00:43:22,450 --> 00:43:22,990 941 00:43:22,990 --> 00:43:24,850 942 00:43:24,850 --> 00:43:27,670 943 00:43:27,670 --> 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973 00:44:47,440 --> 00:44:50,410 974 00:44:50,410 --> 00:44:50,420 975 00:44:50,420 --> 00:44:52,440 976 00:44:52,440 --> 00:44:55,720 977 00:44:55,720 --> 00:44:58,000 978 00:44:58,000 --> 00:45:04,030 979 00:45:04,030 --> 00:45:08,470 980 00:45:08,470 --> 00:45:10,630 981 00:45:10,630 --> 00:45:13,750 982 00:45:13,750 --> 00:45:18,820 983 00:45:18,820 --> 00:45:20,830 984 00:45:20,830 --> 00:45:20,840 985 00:45:20,840 --> 00:45:27,239 986 00:45:27,239 --> 00:45:30,670 987 00:45:30,670 --> 00:45:36,839 988 00:45:36,839 --> 00:45:39,099 989 00:45:39,099 --> 00:45:42,999 990 00:45:42,999 --> 00:45:45,880 991 00:45:45,880 --> 00:45:47,499 992 00:45:47,499 --> 00:45:49,660 993 00:45:49,660 --> 00:45:51,160 994 00:45:51,160 --> 00:45:52,479 995 00:45:52,479 --> 00:45:54,309 996 00:45:54,309 --> 00:45:56,140 997 00:45:56,140 --> 00:45:58,059 998 00:45:58,059 --> 00:46:00,519 999 00:46:00,519 --> 00:46:04,479 1000 00:46:04,479 --> 00:46:06,579 1001 00:46:06,579 --> 00:46:10,509 1002 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00:49:52,840 1088 00:49:52,840 --> 00:49:54,070 1089 00:49:54,070 --> 00:49:57,010 1090 00:49:57,010 --> 00:49:58,390 1091 00:49:58,390 --> 00:50:00,760 1092 00:50:00,760 --> 00:50:02,950 1093 00:50:02,950 --> 00:50:07,240 1094 00:50:07,240 --> 00:50:10,060 1095 00:50:10,060 --> 00:50:12,580 1096 00:50:12,580 --> 00:50:14,350 1097 00:50:14,350 --> 00:50:16,000 1098 00:50:16,000 --> 00:50:18,640 1099 00:50:18,640 --> 00:50:21,430 1100 00:50:21,430 --> 00:50:23,080 1101 00:50:23,080 --> 00:50:25,510 1102 00:50:25,510 --> 00:50:28,600 1103 00:50:28,600 --> 00:50:30,540 1104 00:50:30,540 --> 00:50:32,680 1105 00:50:32,680 --> 00:50:35,380 1106 00:50:35,380 --> 00:50:37,270 1107 00:50:37,270 --> 00:50:41,020 1108 00:50:41,020 --> 00:50:42,340 1109 00:50:42,340 --> 00:50:44,620 1110 00:50:44,620 --> 00:50:46,770 1111 00:50:46,770 --> 00:50:49,390 1112 00:50:49,390 --> 00:50:51,400 1113 00:50:51,400 --> 00:50:53,140 1114 00:50:53,140 --> 00:50:55,570 1115 00:50:55,570 --> 00:50:57,370 1116 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00:52:14,660 1145 00:52:14,660 --> 00:52:16,099 1146 00:52:16,099 --> 00:52:17,450 1147 00:52:17,450 --> 00:52:19,640 1148 00:52:19,640 --> 00:52:22,039 1149 00:52:22,039 --> 00:52:24,829 1150 00:52:24,829 --> 00:52:26,420 1151 00:52:26,420 --> 00:52:29,209 1152 00:52:29,209 --> 00:52:31,789 1153 00:52:31,789 --> 00:52:33,890 1154 00:52:33,890 --> 00:52:35,539 1155 00:52:35,539 --> 00:52:37,219 1156 00:52:37,219 --> 00:52:39,979 1157 00:52:39,979 --> 00:52:41,359 1158 00:52:41,359 --> 00:52:43,069 1159 00:52:43,069 --> 00:52:45,259 1160 00:52:45,259 --> 00:52:48,349 1161 00:52:48,349 --> 00:52:51,319 1162 00:52:51,319 --> 00:53:00,370 1163 00:53:00,370 --> 00:53:00,380 1164 00:53:00,380 --> 00:53:02,440