[1] S. R. Bernfeld, V. Lakshmikantham: An introduction to nonlinear boundary value problems. Academic Press, New York, 1974. MR 0445048 | Zbl 0286.34018

[2] L. Bгüll, H.-P. Hölters: A geometric approach to bifurcation for nonlinear boundary value problems. preprint, Univ. Köln, 1984.

[3] H. Ehrmann: Über die Existenz der Lösungen von Randwertaufgaben bei gewöhnlichen nichtlinearen Differentiaigleichungen zweiter Ordnung. Math. Ann. 134 (1957), pp. 167-194. MR 0092056

[4] H. Ehrmann: Nachweis periodischer Lösungen bei gewissen nichtlinearen Schwingungsdifferentialgleichungen. Arch. Rat. Mech. Anal. 1 (1957), pp. 124-138. MR 0104018 | Zbl 0078.07802

[5] R. E. Gaines, J. Mawhin: Coincidence degree and nonlinear differential equations. Lect. Notes Math. No. 568, Springeг, Berlin, 1977. MR 0637067 | Zbl 0339.47031

[6] J. Mawhin: Topological degree methods in nonlinear boundary value problems. CBMS Regional Conf. Series Math. No. 40, Amer. Math. Soc., Providence, 1979. MR 0525202 | Zbl 0414.34025

[7] J. Mawhin: Compacité, monotonie et convexité dans l'étude de problèmes aux limites semilinéaires. Sémin. Analyse Moderne No. 19, Univ. Sherbrooke, Sherbrooke, 1981.

[8] J. Mawhin: Nonresonance conditions of nonuniform type in nonlinear boundary value problems. in: Dynamical systems II, Academic Press, New Yoгk, 1982, pp. 255-276. MR 0703699 | Zbl 0542.34016

[9] V. A. Pliss: Nonlocal problems of the theory of nonlinear oscillations. Academic Press, New York, 1966. MR 0196199

[10] B. V. Schmitt, N. Sari: Solutions périodiques paires et harmoniques-impaires de l'équation du pendule forcé. J. Méc. Théor. Appl., to appear. MR 0778142 | Zbl 0568.70026

[11] B. V. Schmitt, N. Sari: Sur la structure de l'équation du pendule forcé. to appear. Zbl 0581.70021