In this paper, for an isometric strongly continuous linear representation
denoted by ? of the topological group of the unit circle in complex Banach
space, we study an integral representation for Abel-Poisson mean A?r (x)
of the Fourier coefficients family of an element x, and it is proved that this
family is Abel-Poisson summable to x. Finally, we give some tests which are
related to characterizations of relatively compactness of a subset by means
of Abel-Poisson operator A?r and ?.