Compact Perturbations of Hypercyclic and Supercyclic Operators Domingo HerreroZhi-Qiang Wang Indiana University Mathematics Journal 1990 text pdf 10.1512/iumj.1990.39.39039 10.1512/iumj.1990.39.39039 en Indiana Univ. Math. J. 39 (1990) 819 - 829 state-of-the-art mathematics http://iumj.org/access/