FIRST APPEARANCE OF THE FATOU SET

FATOU, PIERRE.

Séries trigonométriques et séries de Taylor.

Berlin, Stockholm, Paris, F. & G. Beijer, 1906.

4to. Bound in contemporary half cloth with gilt lettering to spine. In "Acta Mathematica", Vol, 30, 1906. Entire volume offered. Stamp to title page, otherwise a fine and clean copy. Pp. 355-400. [Entire volume: 6, 410 pp].

First appearance of Fatou's seminal Ph.D. thesis in which he presented his famous Fatou theorem, which state that a bounded analytic function in the unit disc has radial limits almost everywhere on the unit circle. This theorem was at the origin of a large body of research in 20th-century mathematics under the name of bounded analytic functions. Fatou set is the 'regular' appearance of the chaotic Julia set and both if these initiated what was to be known as "complex dynamics" which eventually resulted in the Mandelbrot set.

Fatou's thesis also include the first application of the Lebesgue integral to concrete problems of analysis, mainly to the study of analytic and harmonic functions in the unit disc. He furthermore studied for the first time the Poisson integral of an arbitrary measure on the unit circle and also made a major contribution to finding a solution to the related question of whether conformal mapping of Jordan regions onto the open disc can be extended continuously to the boundary.

"He contributed important results on the Taylor series, the theory of the Lebesgue integral, and the iteration of rational functions of a complex variable. When studying the circle of convergence of the Taylor series, several points of view are possible: (1) one can look for criteria of convergence or divergence of the series itself on the circumference; (2) one can consider the limit values of the circle of the analytic function represented by the series and try to determine where these limit values are finite or infinite, as well as the properties of the functions of the argument represented by the real and imaginary parts of the series when these functions are well defined; (3) one can consider what points on the circumference, singular in the Weierstrass sense, also determine the analytic extension of the series. The link between these problems led Fatou to formulate a fundamental theorem in the theory of the Lebesgue integral." (DSB).

Order-nr.: 49610