Addition formula for big q-Legendre polynomials
  From Koornwinder's interpretation of big $q$-Legendre polynomials as spherical elements on the quantum $SU(2)$ group an addition formula is derived for the big $q$-Legendre polynomial. The formula involves Al-Salam--Carlitz polynomials, little $q$-Jacobi polynomials and dual $q$-Krawtchouk polynomials. For the little $q$-ultraspherical polynomials a product formula in terms of a big $q$-Legendre polynomial follows by $q$-integration. The addition and product formula for the Legendre polynomials are obtained when $q$ tends to 1. 
Erik Koelink