∀ {X Y : TopCat} {f : X ⟶ Y} (hf : IsOpenMap ⇑(CategoryTheory.ConcreteCategory.hom f))
  ⦃X_1 Y_1 : TopologicalSpace.Opens ↑X⦄ (f_1 : X_1 ⟶ Y_1),
  CategoryTheory.CategoryStruct.comp ((CategoryTheory.Functor.id (TopologicalSpace.Opens ↑X)).map f_1)
      (CategoryTheory.homOfLE ⋯) =
    CategoryTheory.CategoryStruct.comp (CategoryTheory.homOfLE ⋯)
      ((hf.functor.comp (TopologicalSpace.Opens.map f)).map f_1)