Problem ABGT-10. A (gL)-schema for Abelian groups in terms of double inversion. Find an equation A containing a term f(x) or f(y) such that

\{A\} \underleftarrow{=(gL)⇒} \{ \begin{matrix}((x|(((x|y)|z)|(y|e)))|(e|e)) = z \\ f(x) = x \end{matrix} \} .