1. V. I. Arnold, Catastrophe Theory (Znanie, Moscow, 1981; Springer-Verlag, Berlin, 1986); V. I. Arnold, Mathematical Methods of Classical Mechanics (Nauka, Moscow, 1984; Springer-Verlag, Berlin, 1989).
2. E. A. Kuznetsov and V. P. Ruban, Zh. Éksp. Teor. Fiz. 118, 893 (2000) [JETP 91, 775 (2000)].
3. V. A. Zheligovsky, E. A. Kuznetsov, and O. N. Podvigina, Pis’ma Zh. Éksp. Teor. Fiz. 74, 402 (2001) [JETP Lett. 74, 367 (2001)].
4. E. A. Kuznetsov, O. N. Podvigina, and V. A. Zheligovsky, in Proceedings of IUTAH Symposium “Tubes, Sheets, and Singularities in Fluid Dynamics,” Zakopane, 2002 (in press).
5. E. A. Kuznetsov and V. P. Ruban, Pis’ma Zh. Éksp. Teor. Fiz. 67, 1015 (1998) [JETP Lett. 67, 1076 (1998)].