∀ {𝒮 : Type u_2} {𝒳 : Type u_4} [inst : CategoryTheory.Category.{u_3, u_4} 𝒳]
  [inst_1 : CategoryTheory.Category.{u_1, u_2} 𝒮] (p : CategoryTheory.Functor 𝒳 𝒮) {R S : 𝒮} {a b : 𝒳} (f : R ⟶ S)
  (φ : a ≅ b) [inst_2 : p.IsHomLift f φ.hom],
  CategoryTheory.CategoryStruct.comp
      (CategoryTheory.CategoryStruct.comp (CategoryTheory.eqToHom ⋯)
        (CategoryTheory.CategoryStruct.comp (p.mapIso φ).inv (CategoryTheory.eqToHom ⋯)))
      f =
    CategoryTheory.CategoryStruct.id S