1. V. G. Boltyanskii, S. S. Ryshkov, and Yu. A. Shashkin, “On k-regular embeddings and their application to the theory of approximation of functions,” Usp. Mat. Nauk,15, No. 6, 125–132 (1960).
2. S. I. Zukhovitskii and M. G. Krein, “Remark on one possible generalization of the theorems of A. Haar and A. N. Kolmogorov,” Usp. Mat. Nauk,5, No. 1, 217–229 (1950).
3. S. I. Zukhovitskii and S. B. Stechkin, “On the approximation of abstract functions,” Usp. Mat. Nauk,12, No. 1, 187–191 (1957).
4. J. C. Mairhuber, “On Haar's theorem concerning Chebyshev approximation problems having unique solutions,” Proc. Am. Math. Soc.,7, No. 4, 609–615 (1956).
5. C. B. Dunham, “Linear Chebyshev approximation,” Aequat. Math.,10, No. 1, 40–45 (1974).