fact: Definition left_cons_zig_zag {C : category} {x z y : C} (f : x --> z) (gs : zig_zag z y) : zig_zag x y := 1 + length_of_zig_zag gs ,, (z ,, (inl f ,, pr2 gs)).
imports: UniMath.Foundations.All UniMath.MoreFoundations.All UniMath.CategoryTheory.Core.Categories UniMath.CategoryTheory.Core.Isos UniMath.CategoryTheory.Core.Functors UniMath.CategoryTheory.Groupoids