Saddle points and multiple solutions of differential equations

Amann, H., Mancini, G.: Some applications of monotone operator theory to resonance problems. J. Nonlinear Anal. (to appear) Ambrosetti, A., Prodi, G.: Analisi non Lineare. Pisa: Scuola Normale Superiore de Pisa 1973 Ambrosetti, A., Rabinowitz, P.H.: Dual variational methods in critical point theory and applications. J. Functional Analysis14, 349–381 (1973) Brezis, H., Nirenberg, L.: Characterizations of the ranges of some nonlinear operators and applications to boundary value problems. Ann. Scuola Norm. Sup. Pisa, Cl. Sci., Ser. IV,5, 225–326 (1978) Brezis, H., Nirenberg, L.: Forced vibrations for a nonlinear wave equation. Comm. Pure Appl. Math.31, 1–30 (1978) Castro, A.: Hammerstein integral equations with indefinite kernel. Internat. J. Math. & Math. Sci.1, 187–201 (1978) Castro, A., Lazer, A.C.: Applications of a max-min principle. Rev. Colombiana Mat.10, 141–149 (1976) Castro, A., Lazer, A.C.: Critical point theory and the number of solutions of a nonlinear Dirichlet problem. Preprint Clark, D.C.: A variant of the Lusternik-Schnirelman theory. Indiana Univ. Math. J.22, 65–74 (1972) Coffman, C.V.: A minimum-maximum principle for a class of nonlinear integral equations. J. Analyse Math.22, 391–419 (1969) Deimling, K.: Nichtlineare Gleichungen und Abbildungsgrade. Springer Hochschultext, Berlin-Heidelberg-New York: Springer, 1974 Ekeland, I., Temam, R.: Analyse convexe et problèmes variationels. Paris: Dunod 1974 Kransnosel'skii, M.A.: Topological Methods in the Theory of Nonlinear Integral Equations. Oxford-London-New York: Pergamon Press 1964 Lions, J.-L., Magenes, E.: Non-Homogeneous Boundary Value Problems and Applications, I. Berlin-Heidelerg-New York: Springer 1972 Lovicarova, H.: Periodic solutions of a weakly nonlinear wave equation in one dimension. Czechoslowak Math. J.19, 324–342 (1969) Mancini, G.: Periodic solutions of some semilinear autonomous wave equations. Boll. Un. Mat. Ital. B (5)15, 649–672 (1978) Mawhin, J.: Solutions périodiques d'équations aux derivées partielles hyperbolique non linéaire. Rapport No. 84, Institut math. pure appl. Université Catholique de Louvain, 1976 Rabinowitz, P.H.: Periodic solutions of nonlinear hyperbolic partial differential equations. Comm. Pure Appl. Math.20, 145–205 (1967) Rabinowitz, P.H.: Free vibrations for a semilinear wave equation. Comm. Pure Appl. Math.31, 31–68 (1978) Rabinowitz, P.H.: Periodic solutions of Hamiltonian systems. Comm. Pure Appl. Math.31, 157–184 (1978) Rabinowitz, P.H.: A variational method for finding periodic solutions of differential equations. MRC Report 1854, May 1978 Reed, M., Simon, B.: Methods of Modern Mathematical Physics. IV. Analysis of Operators. New York-London: Academic Press 1978 Rockafellar, R.T.: Monotone operators associated with saddle-functions and minimax problems. In: Nonlinear Functional Analysis. Proceedings of Symposia in Pure MathematicsXVIII, Part 1 (Chikago 1968), pp. 241–250. Providence, Rhode Island: American Mathematical Society 1970 Thews, K.: A reduction method for some nonlinear Dirichlet problems. J. Nonlinear Anal. (to appear) Vainberg, M.M.: Variational Methods for the Study of Nonlinear Operators San Francisco: Holden Day 1964 Yosida, K.: Functional Analysis. Berlin-Göttingen-Heidelberg: Springer 1965 Berger, M.S.: Periodic solutions of second order dynamical systems and isoperimetric variational problems. Amer. J. Math.93, 1–10 (1971) Clark, D.C.: On periodic solutions of autonomous Hamiltonian systems of ordinary differential equations. Proc. Amer. Math. Soc.39, 579–584 (1973) Clark, D.C.: Periodic solutions of variational systems of ordinary differential equations. J. Differential Equations28, 354–368 (1978) Thews, K.: Multiple solutions of elliptic boundary value problems with odd nonlinearities. Math. Z.163, 163–175 (1978) Mawhin, J.: Periodic solutions of nonlinear dispersive wave equations. Rapport 120, Inst. de Math., Université Catholique de Louvain, 1978