DENJOY, Leçons sur le Calcul des Coefficients d'une Série Trigonométrique, 1941

First edition.
Three parts on four (the fourth published in 1949)
Arnaud Denjoy (1884-1974), professor at the Faculty of Sciences of the University of Paris, was a leading French mathematician, known for his contributions to the theory of real functions and the Fourier series.
Part One: Mixed Second Differentiation and its application to trigonometric series.
Part Two: Metrics and topology of perfect sets and functions.
Part Three: Determination of a continuous function by its finite extreme generalized second derivative numbers.