proposition: Lemma mulNr x y : (- x) * y = - (x * y).
proof: Proof. by apply: (addrI (x * y)); rewrite -mulrDl !subrr mul0r. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop prime binomial)