1. V.I. Arnold, Sib. Mat. Zh. 28(4), 27–31 (1987).
2. V.I. Arnold, Funkts. Anal. Ego Prilozh. 36, 1–11 (2002).
3. V. I. Arnol’d, in Nonlinear Problems in Mathematical Physics and Related Topics I: In Honor of Professor O.A. Ladyzhenskaya (Kluwer Academic, New York, 2002), Intern. Math. Ser., Vol. 1, pp. 23–34.
4. V. I. Arnold, A. N. Varchenko, and S. M. Gusein-Zade, Singularities of Differentiable Maps (Nauka, Moscow, 1982; Birkhäuser, Boston, 1985), Vol. 1.
5. L. N. Bryzgalova, Funkts. Anal. Ego Prilozh. 11(1), 59–60 (1977).