proposition: Lemma triangle_identity' {C : prebicategory} {a b c : C} (f : a -1-> b) (g : b -1-> c) : right_unitor_2mor f ;h; identity g = inv_from_z_iso (associator f (identity1 b) g) ;v; (identity _ ;h; left_unitor_2mor _).
proof: Proof. refine (!_). use z_iso_inv_on_right. apply triangle_axiom. Qed.
imports: UniMath.Foundations.PartD UniMath.CategoryTheory.Core.Categories UniMath.CategoryTheory.Core.Isos UniMath.CategoryTheory.Core.Univalence UniMath.CategoryTheory.Core.Functors UniMath.CategoryTheory.Core.NaturalTransformations UniMath.CategoryTheory.PrecategoryBinProduct UniMath.CategoryTheory.Categories.StandardCategories UniMath.CategoryTheory.HorizontalComposition UniMath.CategoryTheory.Equivalences.Core