A Note on Non-Quasitriangular Operators II L. Fialkow Indiana University Mathematics Journal 1974 text pdf 10.1512/iumj.1974.23.23018 10.1512/iumj.1974.23.23018 en Indiana Univ. Math. J. 23 (1974) 213 - 220 state-of-the-art mathematics http://iumj.org/access/