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).
Require Import UniMath.Foundations.All. Require Import UniMath.MoreFoundations.All. Require Import UniMath.CategoryTheory.Core.Categories. Require Import UniMath.CategoryTheory.Core.Isos. Require Import UniMath.CategoryTheory.Core.Functors. Require Import UniMath.CategoryTheory.Groupoids.