proposition: Lemma itv_cNyy : `[-oo%E, +oo[%classic = setT :> set (\bar R).
proof: Proof. by rewrite set_itvE predeqE => t; split => //= _; rewrite leNye. Qed.
imports: mathcomp(all_ssreflect ssralg ssrnum ssrint interval) mathcomp(finmap fingroup perm rat) mathcomp(mathcomp_extra boolp classical_sets functions) HB(structures) reals ereal signed topology normedtype sequences