1. M. V. Fedoryuk, Ordinary Differential Equations [in Russian], Nauka, Moscow (1985).
2. R. Gilmore, Catastrophe Theory for Scientists and Engineers, Wiley-Interscience, New York (1981).
3. R. C. Gunning and H. Rossi, Analytic Functions of Several Complex Variables, AMS Chelsea Publ., Providence, Rhode Island (2009).
4. A. M.Ilyin, Matching of Asymptotic Expansions of Solutions of Boundary-Value Problems [in Russian], Nauka, Moscow (1989).
5. A. M. Ilyin and B. I. Suleymanov, “On two special functions related to the cusp catastrophe,” Dokl. Ross. Akad. Nauk, 387, No. 2, 156–158 (2002).