  This paper studies the configuration space of all possible positions of a
linkage in R^n. For example, it shows that for every compact algebraic set,
there is a linkage whose configuration space is analytically isomorphic to a
finite number of copies of the algebraic set. If flexible edges are allowed,
any compact set given by polynomial equalities and inequalities is the
configuration space of a linkage. This paper also characterizes functions which
can be computed by linkages.
