@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://archive.numdam.org/item/CM_1990__74_2_203_0/}
}