1. E. J. Akutowicz:Trans. Am. Math. Soc,83, 179 (1956).
2. E. J. Akutowicz:Proc. Am. Math. Soc,8, 234 (1957).
3. E. C. Titchmarsh:The Theory of Fourier Integrals (Oxford, 1959).
4. E. C. Titchmarsh:The Theory of Functions (Oxford, second edition, 1939).