(** We can now use these facts with [rewrite] and [reflexivity] to give smooth proofs of statements involving equivalences.  Here is a ternary version of the previous [mult_0] result: *)

(* Specifications: *)
Lemma mult_0_3 :
forall n m p, n * m * p = 0 <-> n = 0 \/ m = 0 \/ p = 0.