Unilateral Derivatives of Continuous Functions

The object of this paper is to develop the properties of unilateral derivatives corresponding to those of the derivatives of the ordinary differentiable functions. The general theory of derivatives has not attracted much attention; but some account of derivatives over networks, and derivatives of continuous functions is given in Lebesgtiesche Integrale und Fouriersehe Reihen by Schlesinger and Plessner and other continental books on Function Theory.