@article{NUMA_1973__21_132213,
     author = {Philip M. Anselone and Joel Davis},
     title = {Perturbations of {Best} {Approximation} {Problems.}},
     journal = {Numerische Mathematik},
     pages = {63--69},
     publisher = {mathdoc},
     volume = {21},
     year = {1973},
     zbl = {0264.65009},
     url = {http://geodesic.mathdoc.fr/item/NUMA_1973__21_132213/}
}