∀ {R : Type u_1} [inst : CommRing R] (f g : Polynomial R) (I : Ideal R),
  (AdjoinRoot.quotEquivQuotMap f I) ((Ideal.Quotient.mk (Ideal.map (AdjoinRoot.of f) I)) ((AdjoinRoot.mk f) g)) =
    (Ideal.Quotient.mk (Ideal.span {Polynomial.map (Ideal.Quotient.mk I) f})) (Polynomial.map (Ideal.Quotient.mk I) g)