@article{FAA_1970_4_2_a14,
     author = {D. A. Kazhdan},
     title = {On {A} characteristic of congruence subgroups of the group $G=SL(2,\mathbb{Z})$},
     journal = {Funkcionalʹnyj analiz i ego prilo\v{z}eni\^a},
     pages = {89--90},
     publisher = {mathdoc},
     volume = {4},
     number = {2},
     year = {1970},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/FAA_1970_4_2_a14/}
}