Factorization over Algebras of Subnormal Operators James Thomson Indiana University Mathematics Journal 1988 text pdf 10.1512/iumj.1988.37.37010 10.1512/iumj.1988.37.37010 en Indiana Univ. Math. J. 37 (1988) 191 - 199 state-of-the-art mathematics http://iumj.org/access/