fact: Definition free_gr (X : hSet) : gr := gr_of_monoid (free_gr' X) (invstruct_free_gr X).
imports: UniMath.MoreFoundations.Subtypes UniMath.MoreFoundations.Sets UniMath.Algebra.Monoids UniMath.Algebra.Groups UniMath.Algebra.IteratedBinaryOperations UniMath.Combinatorics.Lists