@article{Abbondandolo_1997, title={A new cohomology for the Morse theory of strongly indefinite functionals on Hilbert spaces}, volume={9}, url={https://apcz.umk.pl/TMNA/article/view/TMNA.1997.017}, abstractNote={A generalized cohomology, similar to Szulkin’s cohomology but with more
general functorial properties, is constructed. This theory is used to
define a relative Morse index and to prove relative Morse relations for
strongly indefinite functionals on Hilbert spaces.}, number={2}, journal={Topological Methods in Nonlinear Analysis}, author={Abbondandolo, Alberto}, year={1997}, month={Jun.}, pages={325–382} }