“…Then, a simple Luenberger-like observer design is feasible for a NOCF, as in Remark 1. We call this problem observer error linearization or the state equivalence to a NOCF which has been studied by many researchers in Besancon (1999), Normand-Cyrot (2003, 2009), Chung and Grizzle (1990), Hou and Pugh (1999), Huijberts (1999), Keller (1987), Krener and Respondek (1985), Lee, Arapostathis, and Marcus (2008), Lee and Hong (2011), Lee and Nam (1991), Lin and Byrnes (1995), Xia and Gao (1988) and Xia and Gao (1989). The observer error linearization problem is a sort of dual concept of the feedback linearization problem.…”