Published online by Cambridge University Press: 20 November 2018
1. Introduction. The averaging operator has an extensive literature, the most detailed account being that of Nörlund
(4). In discussing solutions of the functional relation
1.1
he defines a “principal solution” (4, p. 41) by means of a summability process, and later, working in terms of complex numbers, he obtains (4, p. 70) a principal solution of (1.1) by means of a contour integral. He distinguishes his principal solution from other solutions, by showing that it is continuous at h = 0.