[AK] S. Akbulut and H. King,Topology of real algebraic sets, MSRI Publ.25, Springer-Verlag(1992). [AT] S. Akbulut and L. Taylor,A topological resolution theorem, Publ. I.H.E.S.53, (1981),pp. 163-195 [CR] R. Courant and H. Robbins,What is Mathematics?, Oxford Univ. Press (1941). [K1] H. King,Semicon guration spaces of planar linkages,preprint. [K2] H. King,Con guration spaces of linkages inRn,preprint. [KM] M. Kapovich and J. Millson,Universality Theorems for con guration spaces of planarlinkages,preprint.