1. A. G. Butkovskii, Dokl. Akad. Nauk 227, 309–311 (1976).
2. A. G. Butkovskii, Structural Theory of Distributed Systems (Nauka, Moscow, 1977) [in Russian].
3. A. F. Leont’ev, Entire Functions and Exponential Series (Nauka, Moscow, 1983) [in Russian].
4. Y. Bugeaud, Acta Math. 110, 89–105 (2003).
5. V. G. Sprindzhuk, Usp. Mat. Nauk 35(4), 3–68 (1980).