fact: Definition lwhisker_CAT {C D E : category} (F : [C, D]) {G1 G2 : [D, E]} : [D, E]⟦G1, G2⟧ -> [C, E]⟦functor_compose F G1, functor_compose F G2⟧.
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