Steen Toffner-Clausen, Palle Andersen and Jakob Stoustrup U96-4153· April 18,2001 4th edition Dep artment of Control Engineering, Institute of Electronic Systems Aalborg University, Fredrik Bajers Vej 7, DK-9220 Aalborg O, Denmark !" # $ %# # & ' ( %)# #) # ( % * #* + ' ) #, # + - # . / 0 / 1 &2 ) 3 & '