proposition: Lemma free_abgr_hrel_intro {X : hSet} (l1 l2 : free_gr X) : free_abgr_hrel X (l1 * l2) (l2 * l1).
proof: Proof. apply wittohexists with l1. split with l2. split; reflexivity. Defined.
imports: UniMath.MoreFoundations.Subtypes UniMath.MoreFoundations.Sets UniMath.Algebra.Monoids UniMath.Algebra.Groups UniMath.Algebra.IteratedBinaryOperations UniMath.Combinatorics.Lists