1. Amann, H., Hess, P.: A multiplicity result for a class of elliptic boundary value problems. Proc. R. Soc. Edinb. Sect. A 84(1–2), 145–151 (1979)
2. Amann, H., Zehnder, E.: Nontrivial solutions for a class of nonresonance problems and applications to nonlinear differential equations. Ann. Scuola Norm. Sup. Pisa Cl. Sci. 7(4), 539–603 (1980)
3. Ambrosetti, A.: Elliptic equations with jumping nonlinearities. J. Math. Phys. Sci. 18(1), 1–12 (1984)
4. Ambrosetti, A., Prodi, G.: On the inversion of some differentiable mappings with singularities between Banach spaces. Ann. Mat. Pura Appl. 93(4), 231–246 (1972)
5. Bahri, A.: Résolution générique d’une équation semi-linéaire. C. R. Acad. Sci. Paris Sér. A-B 291(4), A251–A254 (1980)