@article{JRAM_1988__386_153023,
     author = {Andrew M. Winkler},
     title = {Cusp forms and {Hecke} groups.},
     journal = {Journal f\"ur die reine und angewandte Mathematik},
     pages = {187--204},
     publisher = {mathdoc},
     volume = {386},
     year = {1988},
     zbl = {0647.10019},
     url = {http://geodesic.mathdoc.fr/item/JRAM_1988__386_153023/}
}