proposition: Lemma absz_sign s : `|(-1) ^+ s| = 1.
proof: Proof. by rewrite abszX exp1n. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(fintype finfun bigop order ssralg countalg ssrnum) mathcomp(poly)