1. V. P. Maslov, Theory of Perturbations and Asymptotic Methods [in Russian], Moscow State Univ. (1965).
2. V. P. Maslov, Dokl. Akad. Nauk SSSR,123, No. 4, 631?634 (1958).
3. V. P. Maslov and E. M. Vorob'ev, Dokl. Akad. Nauk SSSR,179, No. 3, 558?561 (1968).
4. N. N. Nekhoroshev, Tr. Mosk. Mat. Obshch.,126, 181?198 (1972).
5. M. V. Karasev and V. P. Maslov, Dokl. Akad. Nauk SSSR,257, No. 1, 33?38 (1981).