@article{Agarwal_Filippakis_O‘Regan_Papageorgiou_2008, title={Multiple Solutions for Doubly Resonant Elliptic Problems Using Critical Groups}, volume={10}, url={https://cubo.ufro.cl/ojs/index.php/cubo/article/view/1497}, abstractNote={<p>We consider a semilinear elliptic equation, with a right hand side nonlinearity which may grow linearly. Throughout we assume a double resonance at infinity in the spectral interval [λ<sub>1</sub>, λ<sub>2</sub>]. In this paper, we can also have resonance at zero or even double resonance in the order interval [λ<sub><em>m</em></sub>, λ<em><sub>m</sub></em><sub>+1</sub>], <em>m</em> ≥ 2. Using Morse theory and in particular critical groups, we prove two multiplicity theorems.</p>}, number={3}, journal={CUBO, A Mathematical Journal}, author={Agarwal, Ravi P. and Filippakis, Michael E. and O‘Regan, Donal and Papageorgiou, Nikolaos S.}, year={2008}, month={Oct.}, pages={21–41} }