∀ {X Y : AlgebraicGeometry.Scheme} (f g : X ⟶ Y) (hfg : f = g) (x : ↥X),
  AlgebraicGeometry.Scheme.Hom.stalkMap f x =
    CategoryTheory.CategoryStruct.comp (Y.presheaf.stalkCongr ⋯).hom (AlgebraicGeometry.Scheme.Hom.stalkMap g x)