ABSTRACT
In complex analysis, there exist three distinct approaches to holomorphic function theory of one complex variable. It is well known that these three approaches are equivalent. In 1935, R. Pueter has given a regularity of quaternionic functions as smooth solutions of generalized Cauchy-Riemann equation associated with Laplace equation of four real variables and Pueter and other authors developed a theory of quaternionic regular functions. Also, this theory has been applied to theoretical physics. The chapter aims to give a characterization of Clifford differentiable functions.
