fact: Definition vcomp2_CAT {C D : category} {F G H : [C, D]} : [C,D]⟦F, G⟧ -> [C,D]⟦G, H⟧ -> [C,D]⟦F, H⟧.
imports: UniMath.Foundations.PartD UniMath.MoreFoundations.Tactics UniMath.CategoryTheory.Core.Categories UniMath.CategoryTheory.Core.Functors UniMath.CategoryTheory.Core.Isos UniMath.CategoryTheory.Core.NaturalTransformations UniMath.CategoryTheory.FunctorCategory UniMath.CategoryTheory.whiskering