@article{MAN_1973__206_162518,
     author = {Erik Lippa},
     title = {An {Elementary} {Approach} to {Hecke} {Operators.}},
     journal = {Mathematische Annalen},
     pages = {237--242},
     year = {1973},
     volume = {206},
     zbl = {0251.10022},
     url = {http://geodesic.mathdoc.fr/item/MAN_1973__206_162518/}
}