∀ {C : Type u_2} [inst : CategoryTheory.Category.{u_1, u_2} C] (sq : CategoryTheory.Square C),
  CategoryTheory.CategoryStruct.comp sq.f₃₄ (CategoryTheory.CategoryStruct.id sq.X₄) =
    CategoryTheory.CategoryStruct.comp (CategoryTheory.CategoryStruct.id sq.X₃) sq.f₃₄