@article{IM_1985__80_143234,
     author = {P. Sarnak and R.S. Phillips},
     title = {On cusp forms for co-finite subgroups of {PSL(2,} {IR).}},
     journal = {Inventiones mathematicae},
     pages = {339--364},
     publisher = {mathdoc},
     volume = {80},
     year = {1985},
     zbl = {0558.10017},
     url = {http://geodesic.mathdoc.fr/item/IM_1985__80_143234/}
}