Moscow Aviation Institute, Volokolamskoe shosse, 4, 125871 Moscow, Russia
Bibliografia
[1] V. I. Arnold, S. M. Gusein-Zade and A. N. Varchenko, Singularities of Differentiable Maps, Vol. 1, Nauka, Moscow, 1982 (in Russian); English transl.: Birkhäuser, 1985.
[2] J. F. Nye and A. S. Thorndike, Events in evolving three-dimensional vector fields, J. Phys. A Math. Gen. 13 (1980), 1-14.