proposition: Lemma exprSz x (n : nat) : x ^ n.+1 = x * x ^ n.
proof: Proof. exact: exprS. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(fintype finfun bigop order ssralg countalg ssrnum) mathcomp(poly)