[MathOuvrage]
Contributions to the theory of nonlinear oscillations. Vol. 4
/ Antosiewicz, H. ; Bass, R. ; Bushaw, D. ; Devogelaere, R. ; Kakutani, S. ; Slotnick, D. ; Kyner, W.T. ; Ed. Lefschetz, Solomon ; Markus, Lawrence ; Mendelson, P. ; Seifert, G..
-Princeton NJ : Princeton university Press, 1958. - 211