proposition: Lemma sgzX (n : nat) x : sgz (x ^+ n) = (sgz x) ^+ n.
proof: Proof. by elim: n => [|n IHn]; rewrite ?sgz1 // !exprS sgzM IHn. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(fintype finfun bigop order ssralg countalg ssrnum) mathcomp(poly)