proposition: Lemma distnC m1 m2 : `|m1 - m2| = `|m2 - m1|.
proof: Proof. by rewrite -opprB abszN. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(fintype finfun bigop order ssralg countalg ssrnum) mathcomp(poly)