@article{GDZPPN001171097, title = {Perturbations of Best Approximation Problems.}, journal = {Numerische Mathematik}, volume = {21}, year = {1973}, pages = {63-69}, zbl = {0264.65009}, url = {http://dml.mathdoc.fr/item/GDZPPN001171097} }
Anselone, Philip M.; Davis, Joel. Perturbations of Best Approximation Problems.. Numerische Mathematik, Tome 21 (1973) pp. 63-69. http://gdmltest.u-ga.fr/item/GDZPPN001171097/