Quasi-Nilpotent Equivalence of not Necessarily Commuting Operators I. ColojoaraCiprian Foias Indiana University Mathematics Journal 1966 text pdf 10.1512/iumj.1966.15.15034 10.1512/iumj.1966.15.15034 en Indiana Univ. Math. J. 15 (1966) 521 - 540 state-of-the-art mathematics http://iumj.org/access/