Weak compactness and weak essential spectra of elementary operators Eero Saksman Indiana University Mathematics Journal 1995 text pdf 10.1512/iumj.1995.44.1983 10.1512/iumj.1995.44.1983 en Indiana Univ. Math. J. 44 (1995) 165 - 188 state-of-the-art mathematics http://iumj.org/access/