Series Ultraspheriques et Integrale de Poisson P. Brousse Indiana University Mathematics Journal 1956 text pdf 10.1512/iumj.1956.5.55037 10.1512/iumj.1956.5.55037 en Indiana Univ. Math. J. 5 (1956) 967 - 986 state-of-the-art mathematics http://iumj.org/access/