proposition: Lemma natrelP m n : nat_rels m n (m < n) (n < m) (m == n).
proof: Proof. rewrite ltn_neqAle eqn_leq; case: ltnP; first by constructor. by rewrite leq_eqVlt orbC; case: leqP; constructor; first exact/eqnP. Qed.
imports: mathcomp(ssreflect ssrnat ssrbool eqtype)