Heaviside´s proof of his expansion theorem

J. J. Smith: I should like to refer to the paragraph third from the end of Mr. Vallarta´s paper in which he states that Heaviside gave another alternative proof of his Expansion Formula. This is given in Heaviside´s Electrical Papers, Vol. II, p. 226, in a footnote. As this seems to be another very important way of proving the expansion theorem, I shall take the liberty of quoting it in full, as follows: