@article{MAN_1910__69_158469,
     author = {A. Haar},
     title = {Zur {Theorie} der orthogonalen {Funktionensysteme.} {(Erste} {Mitteilung).}},
     journal = {Mathematische Annalen},
     pages = {331--371},
     publisher = {mathdoc},
     volume = {69},
     year = {1910},
     zbl = {41.0469.03},
     url = {http://geodesic.mathdoc.fr/item/MAN_1910__69_158469/}
}