@article{MAN_1972__199_162314,
     author = {Herbert Amann},
     title = {Lusternik-Schnirelman {Theory} and {Non-Linear} {Eigenvalue} {Problems.}},
     journal = {Mathematische Annalen},
     pages = {55--72},
     publisher = {mathdoc},
     volume = {199},
     year = {1972},
     zbl = {0233.47049},
     url = {http://geodesic.mathdoc.fr/item/MAN_1972__199_162314/}
}