∀ {X Y : AlgebraicGeometry.Scheme} {f : X ⟶ Y},
  (∀ {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)).Etale) →
    AlgebraicGeometry.Etale f