Mapping Properties of the Szego Operator for the Bidisc Peter Knopf Indiana University Mathematics Journal 1989 text pdf 10.1512/iumj.1989.38.38002 10.1512/iumj.1989.38.38002 en Indiana Univ. Math. J. 38 (1989) 59 - 74 state-of-the-art mathematics http://iumj.org/access/