∀ {X Y Z : AlgebraicGeometry.Scheme} (f : X ⟶ Z) (g : Y ⟶ Z) [H : AlgebraicGeometry.IsOpenImmersion f],
  AlgebraicGeometry.PresheafedSpace.IsOpenImmersion
    (CategoryTheory.Limits.pullback.fst (AlgebraicGeometry.Scheme.Hom.toLRSHom g)
        (AlgebraicGeometry.Scheme.Hom.toLRSHom f)).toHom