@article{GDZPPN002306794, title = {Lusternik-Schnirelman Theory and Non-Linear Eigenvalue Problems.}, journal = {Mathematische Annalen}, volume = {196}, year = {1972}, pages = {55-72}, zbl = {0233.47049}, url = {http://dml.mathdoc.fr/item/GDZPPN002306794} }
Amann, Herbert. Lusternik-Schnirelman Theory and Non-Linear Eigenvalue Problems.. Mathematische Annalen, Tome 196 (1972) pp. 55-72. http://gdmltest.u-ga.fr/item/GDZPPN002306794/