@article{JCA_2014_21_3_JCA_2014_21_3_a0,
     author = {P. Mart{\'\i}n and H. Martini and M. Spirova},
     title = {Chebyshev {Sets} and {Ball} {Operators}},
     journal = {Journal of convex analysis},
     pages = {601--618},
     publisher = {mathdoc},
     volume = {21},
     number = {3},
     year = {2014},
     url = {http://geodesic.mathdoc.fr/item/JCA_2014_21_3_JCA_2014_21_3_a0/}
}