∀ {C : Type u₁} [inst : CategoryTheory.Category.{v₁, u₁} C] {D : Type u₂} [inst_1 : CategoryTheory.Category.{v₂, u₂} D]
  {F G : CategoryTheory.Functor C Dᵒᵖ} {E : Type u_1} [inst_2 : CategoryTheory.Category.{v_1, u_1} E]
  {H : CategoryTheory.Functor E C} (α : F ⟶ G) {Z : CategoryTheory.Functor Eᵒᵖ D} (h : (H.comp F).leftOp ⟶ Z),
  CategoryTheory.CategoryStruct.comp (CategoryTheory.NatTrans.leftOp (H.whiskerLeft α)) h =
    CategoryTheory.CategoryStruct.comp (H.leftOpComp G).hom
      (CategoryTheory.CategoryStruct.comp (H.op.whiskerLeft (CategoryTheory.NatTrans.leftOp α))
        (CategoryTheory.CategoryStruct.comp (H.leftOpComp F).inv h))