Published online by Cambridge University Press: 24 October 2008
The conjugate g of a periodic and integrable function f is not necessarily integrable, even when f is monotone inside its fundamental interval. Paley and Wiener, however, proved that g is integrable if f is monotone and odd. A simpler proof was given later by Zygmund‡.
* Suppose for example that the interval is (− π, π), and that
with π − a small.
† Trans. Amer. Math. Soc. 35 (1933), 348–56.Google Scholar
‡ Ibid. 36 (1934), 615–16.
§ Lebesgue integrable over (− ∞, ∞).
* For example,
* There is no special case of Theorem 1 corresponding to it exactly, since f (t) cannot be odd, increasing for all t, and integrable.
† This is not exactly a case of the Paley-Wiener theorem, but becomes one if we consider (0, 2π) instead of (− π, π).
‡ See Hardy, G. H. and Littlewood, J. E., Acta Math. 54 (1930), 99–102;CrossRefGoogle ScholarHardy, G. H., Littlewood, J. E. and Pólya, G., Inequalities, 169,Google Scholar Theorems 240, 241.
§ By theorems of Zygmund and M. Riesz. See Zygmund, , Trigonometrical Series, 150–151.Google Scholar