1. N. V. Efimov and S. B. Stechkin, Some properties of Chebyshev sets, Dokl. AN SSSR,118, No. 1, 17?19 (1958).
2. N. V. Efimov and S. B. Stechkin, Support properties of sets in Banach spaces and Chebyshev sets, Dokl. AN SSSR,127, No. 2, 254?257 (1959).
3. N. V. Efimov and S. B. Stechkin, Approximate compactness and Chebyshev Dokl. AN SSSR,140, No. 3, 522?524 (1961).
4. N. V. Efimov and S. B. Stechkin, Chebyshev sets in Banach spaces, Abstracts of Brief Communications, I. C. M., Stockholm (1962), p. 71.
5. V. L. Klee, Convexity of Chebyshev sets, Math. Ann.,143, 292?304 (1961).