∀ {C : Type u₁} [inst : CategoryTheory.Category.{v₁, u₁} C] {D : Type u₂} [inst_1 : CategoryTheory.Category.{v₂, u₂} D]
  (F : CategoryTheory.Functor C D) {X : C} (S : CategoryTheory.Sieve X) (R : CategoryTheory.Sieve (F.obj X)),
  CategoryTheory.Sieve.functorPushforward F S ≤ R ↔ S ≤ CategoryTheory.Sieve.functorPullback F R