1. S. V. Gonchenko and L. P. Shil'nikov, ?Arithmetic properties of topological invariants of systems with a nongeneric homoclinic trajectory,? Ukr. Mat. Zh.,39, No. 1, 21?28 (1987).
2. A. Kelley, ?The stable, center-stable, center, center-unstable and unstable manifolds,? J. Diff. Equat.,3, No. 4, 546?570 (1967).
3. M. W. Hirsch, C. Pugh and M. Shub, Invariant Manifolds, Lect. Notes in Math., Springer Verlag, Berlin (1983).
4. I. M. Ovsyannikov and L. P. Shil'nikov, ?Systems with a homoclinic curve of saddlefocus type,? Mat. Sb.,130, No. 4, 552?570 (1986).
5. N. K. Gavrilov and L. P. Shil'nikov, ?Three-dimensional dynamical systems close to a system with a nongeneric homoclinic trajectory, I, II,? Mat. Sb.,88, No. 4, 475?492 (1972);90, No. 1, 139?157 (1973).