Proposition double_triangle {C : double_cat} {x y z : C} (h : x -->h y) (k : y -->h z) : lassociator_h h _ k ⋆v (runitor_h h ⋆h id_v_square _) = transportb_square (id_v_left _) (id_v_left _) (id_v_square h ⋆h lunitor_h k). Proof. exact (pr12 (pr222 (pr222 C)) x y z h k). Qed.
Require Import UniMath.MoreFoundations.All. Require Import UniMath.CategoryTheory.Core.Categories. Require Import UniMath.CategoryTheory.Core.Functors. Require Import UniMath.CategoryTheory.Core.NaturalTransformations. Require Import UniMath.CategoryTheory.Core.Isos. Require Import UniMath.CategoryTheory.TwoSidedDisplayedCats.TwoSidedDispCat. Require Import UniMath.CategoryTheory.TwoSidedDisplayedCats.Isos. Require Import UniMath.CategoryTheory.TwoSidedDisplayedCats.Univalence. Require Import UniMath.Bicategories.Core.Examples.BicatOfUnivCats. Require Import UniMath.Bicategories.DoubleCategories.Basics.DoubleCategoryBasics.