  Bleher and Kuijlaars, and Daems and Kuijlaars showed that the correlation
functions of the eigenvalues of a random matrix from unitary ensemble with
external source can be expressed in terms of the Christoffel-Darboux kernel for
multiple orthogonal polynomials. We obtain a representation of this
Christoffel-Darboux kernel in terms of the usual orthogonal polynomials.
