proposition: Lemma dist0n n : `|0 - n| = n.
proof: Proof. by rewrite distnC distn0. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(fintype finfun bigop order ssralg countalg ssrnum) mathcomp(poly)