References
- G. Bonanno, P. Candito, and G. D'aguì, Variational methods on finite dimensional Banach spaces and discrete problems, Adv. Nonlinear Stud. 14 (2014), pp. 915–939.
- F. Flores-Bazán and F. Opazo, Characterizing the convexity of joint-range for a pair of inhomogeneous quadratic functions and strong duality, Minimax Theory Appl. 1 (2016), pp. 257–290.
- P. Pucci and J. Serrin, A mountain pass theorem, J. Differ. Eq. 60 (1985), pp. 142–149.
- B. Ricceri, A strict minimax inequality criterion and some of its consequences, Positivity 16 (2012), pp. 455–470.
- B. Ricceri, Multiplicity theorems involving functions with non-convex range, Stud. Univ. Babeş-Bolyai Math. 68 (2023), pp. 125–137.
- E. Zeidler, Nonlinear Functional Analysis and its Applications, Vol. III, Springer-Verlag, New York, 1985.