fact: Definition RoofMor1Is {x y : ob C} (R : Roof x y) : SOM R x (RoofMor1 R) := pr2 R.
imports: UniMath.Foundations.PartD UniMath.Foundations.Propositions UniMath.Foundations.Sets UniMath.CategoryTheory.Core.Categories UniMath.CategoryTheory.Core.Isos UniMath.CategoryTheory.Core.Functors