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2. and , Elliptic Partial Differential Equations of Second Order (Springer-Verlag, Berlin – Heidelberg – New York, 2001).
3. A general variational principle and some of its applications
4. A multiplicity theorem for the Neumann problem
5. Higher regularity of weak Lq -solutions of the Neumann problem for the Laplacian, Bayreuth. Math. Schr., to appear.