∀ {X Y : AlgebraicGeometry.Scheme} (f : X ⟶ Y) [inst : AlgebraicGeometry.IsOpenImmersion f] (U : X.Opens)
  {Z : AlgebraicGeometry.Scheme} (h : Y ⟶ Z),
  CategoryTheory.CategoryStruct.comp (AlgebraicGeometry.Scheme.Hom.isoImage f U).hom
      (CategoryTheory.CategoryStruct.comp ((AlgebraicGeometry.Scheme.Hom.opensFunctor f).obj U).ι h) =
    CategoryTheory.CategoryStruct.comp U.ι (CategoryTheory.CategoryStruct.comp f h)