fact: Definition Under_precategories_mor_functor_data {c c' : C} (h : C⟦c, c'⟧) : functor_data (c' / C) (c / C).
imports: UniMath.Foundations.PartD UniMath.Foundations.Propositions UniMath.Foundations.Sets UniMath.CategoryTheory.Core.Categories UniMath.CategoryTheory.Core.Functors