@article{GDZPPN002319683, title = {A Cuspidal Class Number Formula for the Modular Curves X1(N).}, journal = {Mathematische Annalen}, volume = {250}, year = {1980}, pages = {197-216}, zbl = {0426.12003}, url = {http://dml.mathdoc.fr/item/GDZPPN002319683} }
Yu, Jing. A Cuspidal Class Number Formula for the Modular Curves X1(N).. Mathematische Annalen, Tome 250 (1980) pp. 197-216. http://gdmltest.u-ga.fr/item/GDZPPN002319683/