@article{MAN_1961__144_160879,
     author = {R. OSSERMAN},
     title = {Hyperbolic surfaces of the form z == f (x, y).},
     journal = {Mathematische Annalen},
     pages = {77--79},
     publisher = {mathdoc},
     volume = {144},
     year = {1961},
     zbl = {0124.29103},
     url = {http://geodesic.mathdoc.fr/item/MAN_1961__144_160879/}
}