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@article{MAT_1968_12_3_a2, author = {Ya. Ihara}, title = {On discrete subgroups of the two by two projective linear group over $\mathfrak p$-adic fields}, journal = {Matematika}, pages = {98--115}, publisher = {mathdoc}, volume = {12}, number = {3}, year = {1968}, language = {ru}, url = {http://geodesic.mathdoc.fr/item/MAT_1968_12_3_a2/} }
Ya. Ihara. On discrete subgroups of the two by two projective linear group over $\mathfrak p$-adic fields. Matematika, Tome 12 (1968) no. 3, pp. 98-115. http://geodesic.mathdoc.fr/item/MAT_1968_12_3_a2/