∀ {X Y : AlgebraicGeometry.Scheme} (f : X ⟶ Y) [self : AlgebraicGeometry.Flat f] {U : Y.Opens},
  AlgebraicGeometry.IsAffineOpen U →
    ∀ {V : X.Opens},
      AlgebraicGeometry.IsAffineOpen V →
        ∀ (e : V ≤ (TopologicalSpace.Opens.map f.base).obj U),
          (CommRingCat.Hom.hom (AlgebraicGeometry.Scheme.Hom.appLE f U V e)).Flat