@article{10_4064_ap_14_2_141_168,
     author = {O. Karwowski},
     title = {Vertical lines and points of a surface},
     journal = {Annales Polonici Mathematici},
     pages = {141--168},
     publisher = {mathdoc},
     volume = {14},
     number = {2},
     year = {1963},
     doi = {10.4064/ap-14-2-141-168},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/ap-14-2-141-168/}
}