intros x y H' H'0; try assumption.
intuition.
elim (INTEGRAL_DOMAIN_prop (x:=x) (y:=y)); auto with algebra.
intros H'1; try assumption.
absurd (Equal y (monoid_unit R)); auto with algebra.
Qed.

(* Specifications: *)
Lemma INTEGRAL_DOMAIN_mult_n0_l :
forall x y : R,
Equal (ring_mult x y) (monoid_unit R) ->
~ Equal x (monoid_unit R) -> Equal y (monoid_unit R).