@article{MM2_1974__14_154302,
     author = {J\"urgen Wolfart and J\"urgen Spilker},
     title = {Untergruppen der {GL2,} welche durch homogene lineare {Kongruenzen} definiert sind.},
     journal = {Manuscripta mathematica},
     pages = {349--378},
     publisher = {mathdoc},
     volume = {14},
     year = {1974},
     zbl = {0297.20053},
     url = {http://geodesic.mathdoc.fr/item/MM2_1974__14_154302/}
}