@article{CMH_1976__51_139677,
     author = {Ted Petrie},
     title = {G {Maps} and the {Projective} {Class} {Group}},
     journal = {Commentarii mathematici Helvetici},
     pages = {611--626},
     publisher = {mathdoc},
     volume = {51},
     year = {1976},
     zbl = {0365.55005},
     url = {http://geodesic.mathdoc.fr/item/CMH_1976__51_139677/}
}