W. J. Walker, "The separation of zeros for entire functions of exponential type," J. Math. Anal. Appl., 122, 257-259 (1987). B. Ya. Levin, Distribution of Roots of Entire Functions [in Russian], Gostekhizdat, Moscow (1956). N. I. Akhiezer, Lectures on Approximation Theory [in Russian], Gostekhizdat, Moscow (1947). G. Hardy, J. Littlewood, and G. Polya, Inequalities [Russian translation], IL, Moscow (1948). V. P. Khavin, "Methods and structure of commutative harmonic analysis," Sovrem. Napravl. Matem. Fundamental'nye Napravl., 15, (1986). M. Plancherel and G. Polya, "Fonctions entiSres et integrals de Fourier multiplies. II," Comment. Math. Helv., 10, 110-163 (1937/38). A. I. Kheifits, "Characteristic of some special classes of entire functions of finite degree," Teor. Funkts. Anal. Prilozhen., 9, 3-13 (1969). A. Zygmund, Trigonometric Series [Russian translation], Vol. II, Mir, Moscow (1965).