@inbook {BP97, title = {On some structural properties of general manipulation systems}, booktitle = {Modelling and Control of Mechanichal Systems}, year = {1997}, pages = {187-202}, publisher = {Imperial College Press}, organization = {Imperial College Press}, address = {London, U.K.}, keywords = {Haptics, Robotics}, author = {A. Bicchi and D Prattichizzo}, editor = {A. Astolfi and D. J. N. Limebeer and C. Melchiorri and A. Tornamb\èe and R.B. Vinter} }