High Quality Content by WIKIPEDIA articles! In mathematics, the Weyl differintegral is an operator defined, as an example of fractional calculus, on functions f on the unit circle having integral 0 and a Fourier series. In other words there is a Fourier series for f of the form anein with a0 = 0, 0, or k-th indefinite integral normalized by integration from = 0. The condition a0 = 0 here plays the obvious role of excluding the need to consider division by zero. The definition is due to Hermann Weyl (1917).