I. Introduction
Stability analysis and control synthesis of nonlinear systems have become more and more important following various practical demands for several decades, and many nonlinear control approaches have been proposed. Among the nonlinear control techniques, Sontag's input-to-state stability (ISS) and its various extension such as integral input-to-state stability (i-ISS) and finite-time input-to-state stability (referring to [9], [7], [8], [10]) provided an effective way to tackle the stabilization of nonlinear systems or the problem of robust/adaptive nonlinear control in the presence of various uncertainties arising from control engineering applications. As of today, many useful results on control design were obtained in the ISS framework (see, e.g., [11], [12], [13], [23]).