Orthogonal polynomials of several discrete variables and the 3nj-Wigner   symbols: applications to spin networks
  The use of orthogonal polynomials for integral models on the lattice is applied to the 3nj-symbols that appear in the coupling of several angular momenta. These symbols are connected to the Ponzano-Regge method to solve the Einstein equations on a discrete Riemannian manifold. 
M. Lorente