Factorization of Operator Valued Entire Functions Marvin RosenblumJames Rovnyak Indiana University Mathematics Journal 1971 text pdf 10.1512/iumj.1971.20.20015 10.1512/iumj.1971.20.20015 en Indiana Univ. Math. J. 20 (1971) 157 - 173 state-of-the-art mathematics http://iumj.org/access/