1. L. Vesely, “Generalized Centres of Finite Sets in Banach Spaces,” Acta Math. Univ. Comenianae
66 (1), 83 (1997).
2. J.-P. Kahane, “Best Approximation in L
1(T)” Bull. Amer. Math. Soc.
80 (5), 788 (1974).
3. P. A. Borodin, “The Linearity Coefficient of Metric Projections onto a Chebyshev Subspace,” Matem. Zametki
85 (2), 180 (2009) [Math. Notes 85 (1), 168 (2009)].
4. K. V. Chesnokova, “The Mapping Sending Three Points of a Banach Space to their Steiner Point,” Vestn. Mosk. Univ. Matem., Mekhan. No. 2, 40 (2016) [Moscow Univ. Math. Bull. 71 (2), 71 (2016)].
5. R. Courant and H. Robbins, What is Mathematics? An Elementary Approach to Ideas and Methods (Oxford University Press, London, 1941; Reg. Khaot. Dinam., Moscow, Izhevsk, 2001).