@misc{CMH_1972__47_186142,
     title = {[unknown]},
     journal = {Commentarii mathematici Helvetici},
     pages = {270--272},
     publisher = {mathdoc},
     volume = {47},
     year = {1972},
     url = {http://geodesic.mathdoc.fr/item/CMH_1972__47_186142/}
}