Comments on "On the stabilization and observation of nonlinear/uncertain dynamic systems

The commenter indicates that stabilization and observation of uncertain and/or nonlinear dynamic systems without matching conditions were investigated in the above-mentioned work by S.H. Zak (see ibid. vol.35, no.5, p.604-7 (1990)). Stabilizing feedback controllers and observers have been proposed. The discussion is based on lemma 1 proved therein. The commenters believe the lemma is incorrect. Since the results presented are based on this lemma, the results are also incorrect. This is indicated by an example and the subsequent discussion. The author admits that lemma 1 is incorrect. Hence, theorem 1 and also theorem 2 which are based on lemma 1 are incorrect. The correct formulation of lemma 1 is presented.<>