Toward a Spectral Characterization of the Set of Norm Limits of Nilpotent Operators of Norm Limits of Nilpotent Operators Domingo Herrero Indiana University Mathematics Journal 1975 text pdf 10.1512/iumj.1975.24.24067 10.1512/iumj.1975.24.24067 en Indiana Univ. Math. J. 24 (1975) 847 - 864 state-of-the-art mathematics http://iumj.org/access/