% This input file is for Otter 3.0.4.
%
% Lemma 0. If a Robbins algebra satisfies 
%
%     exists C, C+C=C,
%
% then it satisfies Huntington's axiom, that is, it is Boolean.
%
% This takes about 20 seconds on a SPARC 5.
%
% The purpose of this job is to construct a proof object that can
% be checked by the proof checker.

op(500, xfy, +).

assign(max_mem, 48000).
assign(max_seconds, 14400).

clear(print_kept).
clear(print_new_demod).
clear(print_back_demod).
% clear(print_given).

assign(pick_given_ratio, 4).
assign(max_weight, 21).

set(knuth_bendix).
set(build_proof_object).

list(usable).
x = x.
end_of_list.

list(sos).
x + y = y + x.
(x + y) + z = x + (y + z).
n(n(x + y) + n(x + n(y))) = x.        % Robbins axiom
C + C = C.                            % hypothesis
n(n(A) + B) + n(n(A) + n(B)) != A.    % denial of Huntington
end_of_list.

list(passive).
end_of_list.