∀ {X Y : AlgebraicGeometry.Scheme} (S : AlgebraicGeometry.Scheme) [inst : X.Over S] [inst_1 : Y.Over S] {f : X ⟶ Y},
  AlgebraicGeometry.Scheme.Hom.IsOver f S ↔ CategoryTheory.CategoryStruct.comp f (Y ↘ S) = X ↘ S