fact: Definition reverse_zig_zag {C : category} {x y : C} (gs : zig_zag x y) : zig_zag y x := length_of_zig_zag gs ,, reverse_zig_zag_of_length (pr2 gs).
imports: UniMath.Foundations.All UniMath.MoreFoundations.All UniMath.CategoryTheory.Core.Categories UniMath.CategoryTheory.Core.Isos UniMath.CategoryTheory.Core.Functors UniMath.CategoryTheory.Groupoids