* {{cite book | author = Khalil, H.K. | year = 1996 | title = Nonlinear systems | publisher = Prentice Hall Upper Saddle River, NJ| isbn = }} | * {{cite book | author = Khalil, H.K. | year = 1996 | title = Nonlinear systems | publisher = Prentice Hall Upper Saddle River, NJ| isbn = }} |