proposition: Lemma cos_geN1 x : -1 <= cos x.
proof: Proof. by rewrite lerNl; have /ler_normlP[] := cos_max x. Qed.
imports: mathcomp(all_ssreflect ssralg ssrint ssrnum matrix) mathcomp(interval rat) mathcomp(mathcomp_extra boolp classical_sets functions) reals ereal nsatz_realtype signed topology normedtype landau sequences derive realfun exp