∀ {X Y : AlgebraicGeometry.Scheme} (f f_1 : X ⟶ Y) (e_f : f = f_1) [H : AlgebraicGeometry.IsOpenImmersion f],
  AlgebraicGeometry.Scheme.Hom.opensFunctor f = AlgebraicGeometry.Scheme.Hom.opensFunctor f_1