fact: Definition functor_ptd_forget : functor category_Ptd [C, C] := tpair _ _ is_functor_ptd_forget.
imports: UniMath.Foundations.PartD UniMath.CategoryTheory.Core.Categories UniMath.CategoryTheory.Core.Functors UniMath.CategoryTheory.Core.NaturalTransformations UniMath.CategoryTheory.FunctorCategory