1. [A] Arnold V. I.: Loss of stability of self-oscillations close to resonance and versal deformations of equivariant vector fields. Funct. Anal. Appl.11 (1977) 85–92
2. [AO] Arnold V.I., Oleinik O.A.: Topology of real algebraic varieties. Moscow University Vestnik (math. series)6 (1976) 7–17 (Russian)
3. Monographs in Mathematics;V.I. Arnold,1986
4. [Aea] Arnold V.I. et. al.: Some unsolved problems in the theory of differential equations and mathematical physics. Russian Math. Surveys44 (1989) 191–202
5. [Bg] Bogdanov R.I.: Versal deformation of a singularity of a vector field on the plane in the case of zero eigenvalues. Seminar Petrovski Proceedings (1976) (Russian). [English translation: Selecta Math. Sovietica1 (1981) 389–421]