@article{IM_1983__71_142983,
     author = {Gopal Prasad and M.S. Raghunathan},
     title = {On the {Congruence} {Subgroups} {Problem:} {Determination} of the },
     journal = {Inventiones mathematicae},
     pages = {21--42},
     publisher = {mathdoc},
     volume = {71},
     year = {1983},
     zbl = {0517.20021},
     url = {http://geodesic.mathdoc.fr/item/IM_1983__71_142983/}
}