∀ {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.Presieve X},
  CategoryTheory.Sieve.generate (CategoryTheory.Presieve.map F s) =
    CategoryTheory.Sieve.functorPushforward F (CategoryTheory.Sieve.generate s)