Nontrivial solutions for resonant noncooperative elliptic systems

In this paper, by introducing some new conditions, we study the nontrivial (multiple) solutions for resonant noncooperative elliptic systems. Our main ingredients are using a new version of Morse theory for strongly indefinite functionals and precisely computing the critical groups of the associated variational functionals at zero and at infinity. © 2000 John Wiley & Sons, Inc.