  An SL_n-character of a group G is the trace of an SL_n-representation of G.
We show that all algebraic relations between SL_n-characters of G can be
visualized as relations between graphs (resembling Feynman diagrams) in any
topological space X, with pi_1(X)=G. We also show that all such relations are
implied by a single local relation between graphs. In this way, we provide a
topological approach to the study of SL_n-representations of groups.
  The motivation for this paper was our work with J. Przytycki on invariants of
links in 3-manifolds which are based on the Kauffman bracket skein relation.
These invariants lead to a notion of a skein module of M which, by a theorem of
Bullock, Przytycki, and the author, is a deformation of the SL_2-character
variety of pi_1(M). This paper provides a generalization of this result to all
SL_n-character varieties.
