fact: Definition post_whisker_in_funcat (B C D : category) {G H : [B, C]} (γ : [B, C]⟦G, H⟧) (K : [C, D]) : [B, D]⟦functor_compose G K, functor_compose H K⟧.
imports: UniMath.Foundations.PartD UniMath.Foundations.Propositions UniMath.Foundations.Sets UniMath.CategoryTheory.Core.Categories UniMath.CategoryTheory.Core.Functors UniMath.CategoryTheory.Core.Isos UniMath.CategoryTheory.Core.NaturalTransformations UniMath.CategoryTheory.FunctorCategory