Spectral Analysis of the Ergodic Hilbert Transform James Campbell Indiana University Mathematics Journal 1986 text pdf 10.1512/iumj.1986.35.35023 10.1512/iumj.1986.35.35023 en Indiana Univ. Math. J. 35 (1986) 379 - 390 state-of-the-art mathematics http://iumj.org/access/