∀ {X : AlgebraicGeometry.Scheme} (U : X.Opens) (x : ↥X) (hxU : x ∈ U) {Z : AlgebraicGeometry.Scheme}
  (h : AlgebraicGeometry.Spec (X.presheaf.obj (Opposite.op U)) ⟶ Z),
  CategoryTheory.CategoryStruct.comp (U.fromSpecStalkOfMem x hxU) (CategoryTheory.CategoryStruct.comp U.toSpecΓ h) =
    CategoryTheory.CategoryStruct.comp (AlgebraicGeometry.Spec.map (X.presheaf.germ U x hxU)) h