proposition: Lemma mulNrn x n : (- x) *+ n = x *- n.
proof: Proof. by elim: n => [|n IHn]; rewrite ?oppr0 // !mulrS opprD IHn. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop prime binomial)