∀ {R : Type u} {S : Type v} {F : Type u_1} [inst : Semiring R] [inst_1 : Semiring S] [inst_2 : FunLike F R S]
  [RingHomClass F R S] (f : F) (s : Set R), Ideal.span (⇑f '' s) = Ideal.map f (Ideal.span s)