“…A tool commonly used in the proof of asymptotic stability are Lyapunov functions with cross terms of the form eg T MðgÞ_ g, e40. This type of functions has been used widely in a number of studies (Berghuis & Nijmeijer, 1993;Chen, Chen, Wang, & Woo, 2001;Kelly, Santibanez, & Reyes, 1998;Loria, Lefeber, & Nijmeijer, 2000;Ortega, Loria, & Kelly, 1995;Pan & Woo, 2000). The motivation here is to construct a Lyapunov function with a derivative containing more negative terms than À_ g T K D _ g, for example the quadratic negative term of the position error.…”