“…Up to now, this fact was established via Lyapunov-like arguments similar to [11] exemplified by, for example, Lemma 5 in [4]; see also Lemma 1 in [12]. However to the best of our knowledge, no Lyapunov function or functional is available so far that proves exponential stability of this system, though a design of such a functional might be of self-interest when treating, for example, system identification, adaptive control, or robustness issue.…”