[1] G. C. Ahuja, T. D. Narang: On best simultaneous approximation. Nieuw Arch. Wisk., 27 (1979), 255-261. MR 0535575 | Zbl 0495.41009

[2] M. W. Bartelt, H. W. McLaughlin: Characterizations of strong unicity in approximation theory. J. Approximation Theory, 9 (1973), 255-266. MR 0372500 | Zbl 0273.41019

[3] C. Franchetti, M. Puri: Some characteristic properties of real Hilbert spaces. Rev. Roum. Math. Pures et Appl. 17 (1972), 1045-1048. MR 0318846

[4] T. D. Narang: On distance sets. Indian J. Pure and Applied Maths., 7 (1976), 1137-1141. MR 0545969 | Zbl 0423.54019

[5] T. D. Narang: Best Approximation and Strict Convexity of Metric Spaces. Arch. Math. 27 (1981), 87-90. MR 0673250 | Zbl 0481.41031

[6] D. V. Pai, P. Veermani: Applications of fixed point theorems to problems in optimization and best approximation. Nonlinear Analysis and Applications, Marcel Dekker, Inc., New York, Edited by S. P. Singh and J. H. Burry (1982), 393-400. MR 0689575

[7] Ivan Singer: Best approximation in normed linear spaces by elements of linear subspaces. Springer-Verlag, 1970. MR 0270044