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2. Ambrosetti, A.: On the existence of multiple solutions for a class of nonlinear boundary value problems. Rend. Sem. Mat. Univ. Padova49, 195?204 (1973)
3. Ambrosetti, A.: A perturbation theorem for superlinear boundary value problems. M.R.C. Techn. Rep.41, No. 41 (1974)
4. Ambrosetti, A., Mancini, G.: Remarks on some free boundary problems. To appear on ?Contributions to nonlinear partial differential equations?. Ed. H. Berestycki, H. Brezis, Pittman
5. Ambrosetti, A., Rabinowitz, P.H.: Dual variational methods in critical point theory and applications. J. Functional Analysis14, 349?381 (1973)