@article{10_4153_CMB_2010_049_7,
     author = {Achter, Jeffrey D.},
     title = {Exceptional {Covers} of {Surfaces}},
     journal = {Canadian mathematical bulletin},
     pages = {385--393},
     year = {2010},
     volume = {53},
     number = {3},
     doi = {10.4153/CMB-2010-049-7},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CMB-2010-049-7/}
}