@article{MAN_1912__71_158516,
     author = {A. Haar},
     title = {Zur {Theorie} der orthogonalen {Funktionensysteme.} {(Zweite} {Mitteilung).}},
     journal = {Mathematische Annalen},
     pages = {38--53},
     publisher = {mathdoc},
     volume = {71},
     year = {1912},
     zbl = {42.0433.01},
     url = {http://geodesic.mathdoc.fr/item/MAN_1912__71_158516/}
}