Applications of the Sz.-Nagy and Foias Lifting Theorem Lavon Page Indiana University Mathematics Journal 1971 text pdf 10.1512/iumj.1971.20.20013 10.1512/iumj.1971.20.20013 en Indiana Univ. Math. J. 20 (1971) 135 - 145 state-of-the-art mathematics http://iumj.org/access/