@article{MZ_1983__184_173368,
     author = {Balz B\"urgisser},
     title = {On the {Projective} {Class} {Group} of {Arithmetic} {Groups.}},
     journal = {Mathematische Zeitschrift},
     pages = {339--358},
     publisher = {mathdoc},
     volume = {184},
     year = {1983},
     zbl = {0505.20033},
     url = {http://geodesic.mathdoc.fr/item/MZ_1983__184_173368/}
}