∀ {X Y : AlgebraicGeometry.LocallyRingedSpace} (f : X ⟶ Y) [H : AlgebraicGeometry.LocallyRingedSpace.IsOpenImmersion f]
  (U : TopologicalSpace.Opens ↑X.toTopCat),
  Opposite.op U =
    (TopologicalSpace.Opens.map f.base).op.obj
      (Opposite.op ((AlgebraicGeometry.LocallyRingedSpace.IsOpenImmersion.opensFunctor f).obj U))