proposition: Lemma signrZK n : @involutive V ( *:%R ((-1) ^+ n)).
proof: Proof. by move=> u; rewrite scalerA -expr2 sqrr_sign scale1r. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop prime binomial)