@article{CMH_1987__62_140086,
     author = {A. Pfister and S. Stolz},
     title = {On the level of projective spaces.},
     journal = {Commentarii mathematici Helvetici},
     pages = {286--291},
     publisher = {mathdoc},
     volume = {62},
     year = {1987},
     zbl = {0634.10020},
     url = {http://geodesic.mathdoc.fr/item/CMH_1987__62_140086/}
}