On strongly indefinite functionals with applications
Helmut Hofer · Transactions of the American Mathematical Society · 1983
Recently, in their remarkable paper Critical point theory for indefinite functionals , V. Benci and P. Rabinowitz gave a direct approach—avoiding finite-dimensional approximations—to the existence theory for critical points of indefinite functionals. In this paper we develop under weaker hypotheses a simpler but more general theory for such problems. In the second part of the paper the abstract results are applied to a class of resonance problems of the Landesman and Lazer type, and moreover they are illustrated by an application to a wave equation problem.