proposition: Lemma mulz2 n : n * 2%:Z = n + n.
proof: Proof. by rewrite -mulrzz. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(fintype finfun bigop order ssralg countalg ssrnum) mathcomp(poly)