@article{MAN_1926__95_159120,
     author = {D. K\"onig and St. Valk\'o},
     title = {\"Uber mehrdeutige {Abbildungen} von {Mengen}},
     journal = {Mathematische Annalen},
     pages = {135--138},
     publisher = {mathdoc},
     volume = {95},
     year = {1926},
     zbl = {51.0165.01},
     url = {http://geodesic.mathdoc.fr/item/MAN_1926__95_159120/}
}