“…To overcome this difficulty, with the effort of many researchers a number of intelligent approaches have been proposed, which can mainly be classified into discontinuous time-invariant stabilization [2,3], smooth timevarying stabilization [4][5][6] and hybrid stabilization [7,8], see the survey paper [9] and references therein for more details. Mainly thanks to these valid approaches, the robust issue of nonholonomic systems has been well-studied and a number of interesting results have been established over the last years, for example, one can see [10][11][12][13][14][15][16][17][18][19][20] and the references therein.…”