Equation (13.65) represents a recursive relationship between a sequence x[n] and its complex cepstrum [n]. Show from Eq. (13.65) that the characteristic system D∗[·] behaves as a causal system for minimum-phase inputs; i.e., show that for minimum-phase inputs, [n] is dependent only on x[k] for k ≤ n. 13.21. Describe a procedure for computing a causal sequence x[n], for which