proposition: Lemma mul0z : left_zero 0 *%Z.
proof: Proof. by case=> [n|[|n]] //=; rewrite muln0. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(fintype finfun bigop order ssralg countalg ssrnum) mathcomp(poly)