1. B. Ya. Levin (B. Ja. Levin), Distribution of Zeros of Entire Functions, Am. Math. Soc, Providence (1964).
2. A. A. Gol'dberg and I. V. Ostrovskii, The Distributions of the Values of MeromorphicFunctions [in Russian], Nauka, Moscow(1970).
3. G. Valiron, “Sur les directions de Borel des fonctions méromorphes d'ordre finie,” J. Math. Pures Appl.,10, 457–480 (1931).
4. A. A. Gol'dberg, “On the growth of an entire function along a ray,” Teor. Funktsii Funktsional. Anal. Prilozhen. (Kharkov), No. 1, 164–175 (1965).
5. W. H. J. Fuchs, “On the growth of meromorphic functions on rays,” in: Studies in Pure Mathematics to the Memory of Paul Turán, Budapest (1983), pp. 219–229.