1. On absolutely convergent exponential sums;Brown, Leon;Trans. Amer. Math. Soc.,1960
2. 2. R. C. Buck, Algebraic properties of classes of analytic functions, Seminars on Analytic Functions, Vol. II, pp. 175-188, Institute for Advanced Study, Princeton, N. J., 1957.
3. Essential boundary points;Rudin, Walter;Bull. Amer. Math. Soc.,1964