@article{JRAM_1992__430_153449,
     author = {R. Weissauer},
     title = {The {Picard} group of {Siegel} modular threefolds.},
     journal = {Journal f\"ur die reine und angewandte Mathematik},
     pages = {179--211},
     publisher = {mathdoc},
     volume = {430},
     year = {1992},
     zbl = {0749.14017},
     url = {http://geodesic.mathdoc.fr/item/JRAM_1992__430_153449/}
}