1. Almansi, E.: Sull'integrazione dell'equazione differenziale ?2n = o. Ann. Mat. Pura Appl. 3 (1899), 2, pp. 1?51
2. Biderman, V. L.: Design of rubber and rubber-cord elements (in Russian). Strength Analysis in Machine Design, 2nd ed., S. D. Ponomarev (Ed.), Vol. 2, 7, pp. 487?491. Moskva: Mashgiz, 1958
3. Dubnov, J. S.: Foundations of vector calculus. Vol. 2 (in Russian), Gos. Izd. Teh.-Teor. Lit., Moskva, 1952
4. Dymnikov, S. J., Pribylov, T. A.: Variational equations of the theory of elasticity for an incompressible medium (in Russian). Editorial Committee Zh. ?Mekhanika Polimerov?; Akad. Nauk Latv. SSR, Riga, 1969
5. Föppl, A., and Föppl, L.: Drang und Zwang, Eine höhere Festigkeitslehre für Ingenieure, 2nd Ed. Vol. 1, München, Berlin, 1924