1. Yu. A. Shashkin, “On convergence of linear operators,” in: Constructive Theory of Functions, Proceedings of International Conference [in Russian], Golden Sands (Varna) (1970);
2. Sofia (1972); pp. 119–125.
3. D. Amir and Z. Ziegler, “Korovkin shadows and Korovkin systems in C(S)-spaces,” J. Math. Appl.,62, No. 3, 640–675 (1978).
4. G. M. Ustinov, “Certain properties of subspaces of the space of affine functions,” Mat. Zametki,17, No. 2, 307–318 (1975).
5. H. H. Shaefer, Toplogical Vector Spaces, Macmillan, London-New York (1966).