Noncommutative Rational Functions and Farber's Invariants of Boundary   Links
  In [2] M. Farber constructed invariants of m-component boundary links with values in algebra of noncommutative rational functions. In this paper we simplify his constructions and express them by using noncommutative generalizations of determinants introduced by Gelfand and Retakh. In particular, for every finite-dimensional module N over the algebra of noncommutative polynomials of m variables we construct a characteristic rational power series chi(N). If N is an algebraically closed field of arbitrary characteristic and N is semisimple, the series chi(N) determines N. 
Vladimir Retakh, Christophe Reutenauer, and Arkady Vaintrob