proposition: Lemma mul1z : left_id 1%Z mulz.
proof: Proof. by case=> [[|n]|n] //=; rewrite ?mul1n// plusE addn0. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(fintype finfun bigop order ssralg countalg ssrnum) mathcomp(poly)