[1] AMBROSETTI A.-RABINOWITZ P. H.: Dual variational methods in critical point theory and applications. J. Funct. Anal. 14 (1973), 369-381. MR 0370183 | Zbl 0273.49063

[2] CHANG K. C.: Variational methods for non-differentiable functionals and their applications to partial differential equations. J. Math. Anal. Appl. 80 (1981), 102-129. MR 0614246 | Zbl 0487.49027

[3] DEGIOVANNI M.: Bifurcation for odd nonlinear variational inequalities. Ann. Fac. Sci. Toulouse Math. (6) 11 (1990), 39-66. MR 1191471

[4] DU Y.: A deformation lemma and some critical point theorems. Bull. Austral. Math. Soc. 43 (1991), 161-168. MR 1086730 | Zbl 0714.58008

[5] GHOUSSOUB N.: A min-max principle with a relaxed boundary condition. Proc. Amer. Math. Soc. 117 (1993), 439-447. MR 1089405 | Zbl 0791.49028

[6] GHOUSSOUB N.-PREISS D.: A general mountain pass principle for locating and classifying critical points. Ann. Inst. H. Poincare. Anal. Non Lineaire 6 (1989), 321-330. MR 1030853 | Zbl 0711.58008

[7] HOFER H.: A note on the topological degree at a critical point of mountainpath-type. Proc. Amer. Math. Soc. 90 (1984), 309-315. MR 0727256

[8] HULSHOF J.-van der VORST R.: Differential systems with strongly indefinite variational structure. J. Funct. Anal. 114 (1993), 97-105. MR 1220982 | Zbl 0793.35038

[9] KAVIAN O.: Introduction á la theorie des points critiques et applications aux problémes elliptiques. Mathématiques & Applications 13, Springer Verlag, Paris, 1993. MR 1276944 | Zbl 0797.58005

[10] KUBRULSKI R. S.: Variational methods for nonlinear eigenvalue problems. Differential Integral Equations 3 (1990), 923-932.

[11] LEFTER C.-MOTREANU D.: Critical point theory in nonlinear eigenvalue problems with discontinuities. In.: Internat. Ser. Numer. Math. 107, Birkhäuser Verlag, Basel, 1992, pp. 25-36. MR 1223355

[12] MOTREANU D.: Existence for minimization with nonconvex constraints. J. Math. Anal. Appl. 117 (1986), 128-137. MR 0843009 | Zbl 0599.49008

[13] MOTREANU D.-PANAGIOTOPOULOS P. D.: Hysteresis: the eigenvalue problem for hemivariational inequalities. In: Models of Hysteresis, Longman Scient. PubL, Harlow, 1993, pp. 102-117. MR 1235118 | Zbl 0801.49027

[14] PALAIS R. S.: Lusternik-Schnirelman theory on Banach manifolds. Topology 5 (1966), 115-132. MR 0259955 | Zbl 0143.35203

[15] PALAIS R. S.-TERNG C. L.: Critical Point Theory and Submanifold Geometry. Lecture Notes in Math. 1353, Springer Verlag, Berlin, 1988. MR 0972503 | Zbl 0658.49001

[16] RABINOWITZ P. H.: Variational methods for nonlinear eigenvalue problems. In: Eigenvalues of Nonlinear Problems (G. Prodi, ed.), C.I.M.E., Edizioni Cremonese, Roma, 1975, pp. 141-195. MR 0464299

[17] RABINOWITZ P. H.: Minimax Methods in Critical Point Theory With Applications to Differential Equations. CBMS Regional Conf. Ser. in Math. 65, Amer.Math.Soc, Providence, R.I., 1986. MR 0845785 | Zbl 0609.58002

[18] RAUCH J.: Discontinuous semilinear differential equations and multiple valued maps. Proc. Amer. Math. Soc. 64 (1977), 277-282. MR 0442453 | Zbl 0413.35031

[19] SCHECHTER M.-TINTAREV K.: Spherical maxima in Hilbert space and semilinear elliptic eigenvalue problems. Differential Integral Equations 3 (1990), 889-899. MR 1059337 | Zbl 0727.35105

[20] SCHECHTER M.-TINTAREV K.: Points of spherical maxima and solvability of semilinear elliptic equations. Canad. J. Math. 43 (1991), 825-831. MR 1127032 | Zbl 0755.35083

[21] SZULKIN A.: Minimax principles for lower semicontinuous functions and applications to nonlinear boundary value problems. Ann. Inst. H. Poincaré Anal. Non Lineaire 3 (1986), 77-109. MR 0837231 | Zbl 0612.58011

[22] SZULKIN A.: Ljusternik-Schnirelman theory on $C^1$-manifold. Ann. Inst. H. Poincaré Anal Non Linéaire 5 (1988), 119-139. MR 0954468

[23] WANG T.: Ljusternik-Schnirelman category theory on closed subsets of Banach manifolds. J. Math. Anal. Appl. 149 (1990), 412-423. MR 1057683

[24] ZEIDLER E.: Ljusternik-Schnirelman theory on general level sets. Math. Nachr. 129 (1986), 235-259. MR 0864637 | Zbl 0608.58014