1. J. Ackermann, Sampled-Data Control Systems, Springer-Verlag, Berlin, 1985.
2. P. M. Cohn, Free Rings and their Relations, Academic Press, London, 1985.
3. SIAM J. Control Optimiz.;JM Coron,1993
4. Proc. IFAC-Symposium NOLCOS’92, Bordeaux;E Delaleau,1992
5. E. Delaleau and W. Respondek, Removing input derivatives and lowering their orders in generalized state-space representations. In Proc. 31st IEEE Control Decision Conf., Tucson. (1991)