1. Bereanu C., Mawhin J.: Boundary value problems with non-surjective ϕ-Laplacian and one-side bounded nonlinearity. Adv. Differ. Eqs. 11, 35–60 (2006)
2. Bonanno G.: A critical point theorem via the Ekeland variational principle. Nonlinear Anal. 75, 2992–3007 (2012)
3. Bonanno G., D’Aguì G.: Critical nonlinearities for elliptic Dirichlet problems. Dyn. Syst. Appl. 22, 411–417 (2013)
4. Bonanno, G., Livrea, R.: Existence and multiplicity of periodic solutions for second order Hamiltonian systems depending on a parameter. J. Convex Anal. 20(4), 1075–1094 (2013)
5. Bonanno G., Pizzimenti P.: Existence results for nonlinear elliptic problems. Appl. Anal. 92, 411–423 (2013)