Remark 1. The models (1) and (2) are able to represent almost all chaotic systems. Therefore, the synchronization schemein this paper is extensively applicable almost to all the chaotic systems, and even other control problems consideringunknown control direction and input saturation. What’s more, as pointed out in [25], the method is also applicable toother nonlinearities which can be approximated by a bounded smooth nonlinear function.