Observer Design for a General Class of Nonlinear Systems
  The paper deals with the observer design problem for a wide class of triangular nonlinear time-varying systems. The results of the present work generalize previous results in the literature dealing with the observer design problem for triangular systems and particularly, constitute generalizations of those obtained in a recent authors work concerning a class of triangular systems, whose dynamics have p-normal form. 
Dimitris Boskos, John Tsinias
math.OC