@article{GDZPPN00226949X, title = {A property of Haar's system of orthogonal functions.}, journal = {Mathematische Annalen}, volume = {90}, year = {1923}, pages = {38-45}, zbl = {49.0293.02}, url = {http://dml.mathdoc.fr/item/GDZPPN00226949X} }
Walsh, J.L. A property of Haar's system of orthogonal functions.. Mathematische Annalen, Tome 90 (1923) pp. 38-45. http://gdmltest.u-ga.fr/item/GDZPPN00226949X/