@article{JCA_2007_14_1_JCA_2007_14_1_a11,
     author = {D. Pavlica and L. Zaj{\'\i}cek},
     title = {On the {Directions} of {Segments} and {r-Dimensional} {Balls} on a {Convex} {Surface}},
     journal = {Journal of convex analysis},
     pages = {149--167},
     publisher = {mathdoc},
     volume = {14},
     number = {1},
     year = {2007},
     url = {http://geodesic.mathdoc.fr/item/JCA_2007_14_1_JCA_2007_14_1_a11/}
}