∀ {C : Type u₁} [inst : CategoryTheory.Category.{v₁, u₁} C] {D : Type u₂} [inst_1 : CategoryTheory.Category.{v₂, u₂} D]
  {F G : CategoryTheory.Functor C D} (self : CategoryTheory.NatTrans G F) ⦃X Y : C⦄ (f : Y ⟶ X) {Z : D}
  (h : Z ⟶ G.obj Y),
  CategoryTheory.CategoryStruct.comp (CategoryTheory.CategoryStruct.comp h (self.app Y)) (F.map f) =
    CategoryTheory.CategoryStruct.comp (CategoryTheory.CategoryStruct.comp h (G.map f)) (self.app X)