@article{CMH_1989__64_1_140177,
     author = {Stephan Stolz},
     title = {The level of real projective spaces.},
     journal = {Commentarii mathematici Helvetici},
     pages = {661--674},
     publisher = {mathdoc},
     volume = {64},
     number = {1},
     year = {1989},
     zbl = {0697.55009},
     url = {http://geodesic.mathdoc.fr/item/CMH_1989__64_1_140177/}
}