Rational decompositions of complex meromorphic functions
  Let h be a complex meromorphic function decomposed in two different ways P(f) and Q(g), where f, g are meromorphic functions and P, Q are rational functions. We follow an approach due to C.-C. Yang, P. Li and K. H. Ha who handle similar decompositions, however, with P, Q polynomials, by applying the Second Nevanlinna Theorem. We establish relations between the number k of distinct zeros of P', the degrees of P and Q, and (unless f, g are analytic functions) the number of distinct zeros of the denominators of P and Q. 
Alain Escassut and Eberhard Mayerhofer