proposition: Lemma eq_ptd_mor {F G : ptd_obj} (a b : ptd_mor F G) : a = b ≃ (a : F ⟹ G) = b.
proof: Proof. apply subtypeInjectivity. intro x. apply impred; intro. apply homset_property. Defined.
imports: UniMath.Foundations.PartD UniMath.CategoryTheory.Core.Categories UniMath.CategoryTheory.Core.Functors UniMath.CategoryTheory.Core.NaturalTransformations UniMath.CategoryTheory.FunctorCategory