1. V. I. Arnol'd, A. N. Varchenko, and S. M. Gusein-Zade, Singularities of Differentiable Mappings [in Russian], Vol. I, Nauka, Moscow (1982).
2. V. I. Arnol'd, A. N. Varchenko, and S. M. Gusein-Zade, Singularities of Differentiable Mappings [in Russian], Vol. II, Nauka, Moscow (1983).
3. F. S. Berezovskaya, ?The index of a stationary point of a vector field on the plane,? Funkts. Anal. Prilozhen.,13, No. 2, 77 (1979).
4. D. N. Bernshtein, ?The number of roots of a system of equations,? Funkts. Anal. Prilozhen.,9, No. 3, 1?4 (1975).
5. A. G. Kushnirenko and A. G. Khovanskii, ?Newton polyhedra,? Usp. Mat. Nauk,31, No. 2, 201?202 (1976).