proposition: Proposition double_triangle' {C : double_cat} {x y z : C} (h : x -->h y) (k : y -->h z) : transportf_square (id_v_left _) (id_v_left _) (lassociator_h h _ k ⋆v (runitor_h h ⋆h id_v_square _)) = id_v_square h ⋆h lunitor_h k.
proof: Proof. rewrite double_triangle. rewrite transportfb_square. apply idpath. Qed.
imports: UniMath.MoreFoundations.All UniMath.CategoryTheory.Core.Categories UniMath.CategoryTheory.Core.Functors UniMath.CategoryTheory.Core.NaturalTransformations UniMath.CategoryTheory.Core.Isos UniMath.CategoryTheory.TwoSidedDisplayedCats.TwoSidedDispCat UniMath.CategoryTheory.TwoSidedDisplayedCats.Isos UniMath.CategoryTheory.TwoSidedDisplayedCats.Univalence UniMath.Bicategories.Core.Examples.BicatOfUnivCats UniMath.Bicategories.DoubleCategories.Basics.DoubleCategoryBasics