In this paper my object is, primarily, to investigate the properties of a certain operative symbol which appears to be of great utility in discussing q -functions. The first part of the paper will consist of an investigation into the various forms of and the nature of the inverse operations symbolised by Δ − n . With certain restrictions as to continuity, etc., φ( x ) will denote an arbitrary function of x .
F. H. Jackson (Fri,) studied this question.