∀ {X Y : AlgebraicGeometry.Scheme} (f : X ⟶ Y) [inst : AlgebraicGeometry.QuasiCompact f]
  [inst_1 : AlgebraicGeometry.QuasiSeparated f] {U : Y.Opens},
  (TopologicalSpace.Opens.map f.base).obj U ≤
    (TopologicalSpace.Opens.map (AlgebraicGeometry.Scheme.Hom.toNormalization f).base).obj
      ((TopologicalSpace.Opens.map (AlgebraicGeometry.Scheme.Hom.fromNormalization f).base).obj U)