intros z1 z2; case z1; case z2; simpl in |- *; intros; auto; try discriminate.
Qed.
Hint Resolve NotZmultZero: zarith.
(* Conversions from R <-> Z  <-> N *)

Theorem IZR_zero : forall p : Z, p = 0%Z -> IZR p = 0%R.
intros p H'; rewrite H'; auto.