A recursion formula for the correlation functions of an inhomogeneous   XXX model
  A new recursion formula is presented for the correlation functions of the integrable spin 1/2 XXX chain with inhomogeneity. It relates the correlators involving n consecutive lattice sites to those with n-1 and n-2 sites. In a series of papers by V. Korepin and two of the present authors, it was discovered that the correlators have a certain specific structure as functions of the inhomogeneity parameters. Our formula allows for a direct proof of this structure, as well as an exact description of the rational functions which has been left undetermined in the previous works. 
H. Boos, M. Jimbo, T. Miwa, F. Smirnov and Y. Takeyama