%0 Journal Article
%A Ted Petrie
%T G Maps and the Projective Class Group
%J Commentarii mathematici Helvetici
%D 1976
%P 611-626
%V 51
%I mathdoc
%U http://geodesic.mathdoc.fr/item/CMH_1976__51_139677/
%F CMH_1976__51_139677