@article{10_4153_CMB_2002_033_1,
     author = {Sebbar, Abdellah},
     title = {Modular {Subgroups,} {Forms,} {Curves} and {Surfaces}},
     journal = {Canadian mathematical bulletin},
     pages = {294--308},
     year = {2002},
     volume = {45},
     number = {2},
     doi = {10.4153/CMB-2002-033-1},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CMB-2002-033-1/}
}