@article{AM_2001_153_1_a3,
     author = {J. Lewis and D. Zagier},
     title = {Period functions for {Maass} wave forms. {I}},
     journal = {Annals of mathematics},
     publisher = {mathdoc},
     volume = {153},
     number = {1},
     year = {2001},
     url = {http://geodesic.mathdoc.fr/item/AM_2001_153_1_a3/}
}