On the Kronecker Product of Irreducible Unitary Representations of the Inhomogeneous Lorentz Group Lajos Pukainszky Indiana University Mathematics Journal 1961 text pdf 10.1512/iumj.1961.10.10030 10.1512/iumj.1961.10.10030 en Indiana Univ. Math. J. 10 (1961) 475 - 491 state-of-the-art mathematics http://iumj.org/access/