proposition: Lemma distn0 n : `|n - 0| = n.
proof: Proof. by rewrite subr0 absz_nat. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(fintype finfun bigop order ssralg countalg ssrnum) mathcomp(poly)