∀ {X : Type u} [inst : Preorder X] {a b c : X} (hab : b ≤ a) (hbc : Opposite.op b = Opposite.op c) {Z : Xᵒᵖ}
  (h : Opposite.op c ⟶ Z),
  CategoryTheory.CategoryStruct.comp (CategoryTheory.homOfLE hab).op
      (CategoryTheory.CategoryStruct.comp (CategoryTheory.eqToHom hbc) h) =
    CategoryTheory.CategoryStruct.comp (CategoryTheory.homOfLE ⋯).op h