fact: Definition left_extension : UU := ∑ (h : y --> z) (τ : f ==> g · h), is_left_extension τ.
imports: UniMath.Foundations.All UniMath.MoreFoundations.All UniMath.CategoryTheory.Core.Prelude UniMath.Bicategories.Core.Bicat UniMath.Bicategories.Core.Examples.OpMorBicat UniMath.Bicategories.Core.Examples.OpCellBicat