proposition: Lemma fginv_fginv {X : hSet} (l : free_monoid (setcoprod X X)) : fginv (fginv l) = l.
proof: Proof. unfold fginv. rewrite map_reverse, reverse_reverse, <- map_compose, <- map_idfun. apply map_homot. exact coprodcomm_coprodcomm. Defined.
imports: UniMath.MoreFoundations.Subtypes UniMath.MoreFoundations.Sets UniMath.Algebra.Monoids UniMath.Algebra.Groups UniMath.Algebra.IteratedBinaryOperations UniMath.Combinatorics.Lists