Critical points when there is no saddle point geometry
Using the topological method of linking subsets [the author and \textit{K. Tintarev}, Bull. Soc. Math. Belg., Sér. B 44, 249-261 (1992; Zbl 0785.58017)]the author proves two abstract theorems that imply certain extensions of the saddle point theorem of \textit{P. H. Rabinowitz} [Reg. Conf. Ser. Math. 65 (1986; Zbl 0609.58002)]. The results are then used to obtain the existence of nontrivial solutions of semilinear elliptic boundary value problems of the form \(Au=f(x,u)\).
scientific article; zbMATH DE number 929672