@article{MZ_1990__204_3_183775,
     author = {Thomas Bartsch and M\'onica Clapp},
     title = {Bifurcation {Theory} for {Symmetric} {Potential} {Operators} and the {Equvariant} {Cup-length.}},
     journal = {Mathematische Zeitschrift},
     pages = {341--356},
     publisher = {mathdoc},
     volume = {204},
     number = {3},
     year = {1990},
     zbl = {0682.58037},
     url = {http://geodesic.mathdoc.fr/item/MZ_1990__204_3_183775/}
}