@article{JRAM_1986__365_152810,
     author = {Avner Ash and Glenn Stevens},
     title = {Cohomology of arithmetic groups and congruences between systems of {Hecke} eigenvalues.},
     journal = {Journal f\"ur die reine und angewandte Mathematik},
     pages = {192--220},
     publisher = {mathdoc},
     volume = {365},
     year = {1986},
     zbl = {0596.10026},
     url = {http://geodesic.mathdoc.fr/item/JRAM_1986__365_152810/}
}