@article{CMH_1979__54_139787,
     author = {Jens Frehse},
     title = {A {Landesman-Lazer} alternative theorem for a class of optimization problems.},
     journal = {Commentarii mathematici Helvetici},
     pages = {328--333},
     publisher = {mathdoc},
     volume = {54},
     year = {1979},
     zbl = {0431.49003},
     url = {http://geodesic.mathdoc.fr/item/CMH_1979__54_139787/}
}