fact: Definition RoofMor1 {x y : ob C} (R : Roof x y) : C⟦R, x⟧ := dirprod_pr1 (pr2 (pr1 R)).
imports: UniMath.Foundations.PartD UniMath.Foundations.Propositions UniMath.Foundations.Sets UniMath.CategoryTheory.Core.Categories UniMath.CategoryTheory.Core.Isos UniMath.CategoryTheory.Core.Functors