proposition: Lemma subz_ge0 m n : lez 0 (n - m) = lez m n.
proof: Proof. case: (intP m); case: (intP n)=> // {}m {}n /=; rewrite ?ltnS -?opprD ?opprB ?subzSS; case: leqP=> // hmn; by [ rewrite subzn // | rewrite -opprB subzn ?(ltnW hmn) //; move: hmn; rewrite -subn_gt0; case: (_ - _)%N]. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(fintype finfun bigop order ssralg countalg ssrnum) mathcomp(poly)