“…In [5], Phillips and the present writer have considered the first-and second-order cases by a general operator-theoretic approach developed by Phillips in [2] and [3]. That it has been possible, in the general case treated in the present paper, to obtain all the information obtained in [1], [4], [5] by using the operator-theoretic approach is an indication of the power of that method. The author wishes to express his gratitude to Professor Ralph Phillips for suggesting this more general investigation, for his inspiration, and for his helpful criticisms and encouragement in the preparation of this paper, and also to the referee for his suggestions.…”