“…In particular, robust tracking and disturbance rejection of any given continuous periodic reference and disturbance signals y * ref (t) and w * (t), respectively, can be formulated as a robust output regulation problem for an infinite-dimensional exosystem [12,15]. Tracking of nonsmooth periodic and almost periodic signals with high accuracy is necessary, e.g., in the control of disk drive systems and robot arms [29,10], and in power electronics [3].Recent years have seen many succesful efforts in the development of the state space theory of robust output regulation for distributed parameter systems with infinite-dimensional exosystems [11,16,9,19]. In particular, the p-copy internal model principle of Francis and Wonham [7], and Davison [5] was extended for infinite-dimensional linear systems by the current authors in [16].…”