∀ {C : Type u_1} [inst : CategoryTheory.Category.{u_2, u_1} C] {A : Type u_4}
  [inst_1 : CategoryTheory.Category.{u_3, u_4} A] (F G : CategoryTheory.Functor Cᵒᵖ A) (X : Cᵒᵖ),
  (CategoryTheory.Over.map (CategoryTheory.CategoryStruct.id X).unop).op.whiskerLeft =
    CategoryTheory.CategoryStruct.id
      ((CategoryTheory.Over.forget (Opposite.unop X)).op.comp F ⟶
        (CategoryTheory.Over.forget (Opposite.unop X)).op.comp G)