@article{CMH_1984__59_139978,
     author = {John K. Beem and Philipp E. Parker},
     title = {Values of pseudoriemannian sectional cuvature.},
     journal = {Commentarii mathematici Helvetici},
     pages = {319--332},
     publisher = {mathdoc},
     volume = {59},
     year = {1984},
     zbl = {0573.53014},
     url = {http://geodesic.mathdoc.fr/item/CMH_1984__59_139978/}
}