@article{10_4064_aa_85_3_197_207,
     author = {Nobuhiko Ishida},
     title = {Generators and equations for modular function fields of principal congruence subgroups},
     journal = {Acta Arithmetica},
     pages = {197--207},
     publisher = {mathdoc},
     volume = {85},
     number = {3},
     year = {1998},
     doi = {10.4064/aa-85-3-197-207},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/aa-85-3-197-207/}
}