“…The classic problem of output regulation, which includes as special cases the problems of reference tracking and disturbance rejection when references/disturbances are deterministically generated by an exogenous system, is one of the key problems in control theory, perhaps second just to the stabilization problem. For this reason a lot of efforts have been devoted to solve this problem, starting from the classic linear time invariant (LTI) setting considered in [1], [2], [3], and then considering the nonlinear setting [4], [5], [6], the use of adaptive or data driven mechanisms to estimate the exosystem's frequencies [7], [8], [9], the realization using an external (as opposed to internal) device still satisfying the internal model principle [10], [11], [12], [13], [14], and contribution considering other structural features or constraints, like saturations on inputs and outputs [15] or overactuation [16], [17], [18], [19].…”