proposition: Lemma mul2z n : 2%:Z * n = n + n.
proof: Proof. by rewrite mulrC -mulrzz. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(fintype finfun bigop order ssralg countalg ssrnum) mathcomp(poly)