Contributions to the theory of nonlinar oscillations - Antosiewicz, H; Bass, R; Bushaw, D; DeVogelaere, R; Kakutani, S; Kyner, W. T; Lefschetz, Solomon; Markus, L; Mendelson, P; Seifert, G; Slotnick, D (Annals of Mathematics Studies, 41, 1958)