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 links 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. The formula mentioned above makes it possible to prove this structure directly, as well as to obtain an exact description of the rational functions that were left undetermined in the earlier work.