@article{CM_1990__76_1-2_87_0,
     author = {Feustel, Jan},
     title = {Eine {Klassenzahlformel} f\"ur singul\"are {Moduln} der {Picardschen} {Modulgruppen}},
     journal = {Compositio Mathematica},
     pages = {87--100},
     publisher = {Kluwer Academic Publishers},
     volume = {76},
     number = {1-2},
     year = {1990},
     mrnumber = {1078859},
     zbl = {0732.14016},
     language = {de},
     url = {http://www.numdam.org/item/CM_1990__76_1-2_87_0/}
}