@article{MAN_1975__216_162734,
     author = {Eberhard Freitag},
     title = {Holomorphe {Differentialformen} zu {Kongruenzgruppen} der {Siegeischen} {Modulgruppe} zweiten {Grades.}},
     journal = {Mathematische Annalen},
     pages = {155--164},
     publisher = {mathdoc},
     volume = {216},
     year = {1975},
     zbl = {0307.32026},
     url = {http://geodesic.mathdoc.fr/item/MAN_1975__216_162734/}
}