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@article{CM_1990__74_2_203_0, author = {Elkies, Noam D.}, title = {The automorphism group of the modular curve $X_0(63)$}, journal = {Compositio Mathematica}, pages = {203--208}, publisher = {Kluwer Academic Publishers}, volume = {74}, number = {2}, year = {1990}, mrnumber = {1047740}, zbl = {0708.14016}, language = {en}, url = {http://geodesic.mathdoc.fr/item/CM_1990__74_2_203_0/} }
Elkies, Noam D. The automorphism group of the modular curve $X_0(63)$. Compositio Mathematica, Tome 74 (1990) no. 2, pp. 203-208. http://geodesic.mathdoc.fr/item/CM_1990__74_2_203_0/