1. L. P. Vlasov, “Approximative properties of sets in normed linear spaces,” Usp. Mat. Nauk, 28, No.6, 3–66 (1973); English transl. Russian Math. Surveys, 28, No. 6, 1–66 (1973).
2. V. A. Koshcheev, “The connectivity and approximative properties of sets in linear normed spaces,” Mat. Zametki, 17, No.2, 193–204 (1975); English transl. Math. Notes, 17, No. 2, 114–119 (1975).
3. V. A. Koshcheev, “Connectedness and solar properties of sets in normed linear spaces,” Mat. Zametki, 19, No.2, 267–278 (1976); English transl. Math. Notes, 19, No. 2, 158–164 (1976).
4. A. L. Brown, “Suns in normed linear spaces which are finite dimensional,” Math. Ann., 279, 81–101 (1987).
5. A. L. Garkavi, “The theory of best approximation in normed linear spaces,” In: Itogi Nauki i Tekhniki, Matem. Analiz, 1967 [in Russian], VINITI, Moscow, 1969, pp. 75–132; English transl. Progr. Math., Vol. 8: Mathematical Analysis, 1970, pp. 83–150.