@article{MZ_1920__6_167561,
     author = {K., Knopp},
     title = {Mittelwertbildung und {Reihentransformation}},
     journal = {Mathematische Zeitschrift},
     pages = {118--123},
     publisher = {mathdoc},
     volume = {6},
     year = {1920},
     zbl = {47.0202.01},
     url = {http://geodesic.mathdoc.fr/item/MZ_1920__6_167561/}
}