∀ {X Y : AlgebraicGeometry.Scheme} (f : X ⟶ Y) [AlgebraicGeometry.FormallyUnramified f]
  [AlgebraicGeometry.LocallyOfFiniteType f] (x : ↥X), Algebra.IsSeparable ↑(Y.residueField (f x)) ↑(X.residueField x)