Saturation Theorems Related to the Mean Ergodic Theorem D. Leviatan Indiana University Mathematics Journal 1975 text pdf 10.1512/iumj.1975.24.24005 10.1512/iumj.1975.24.24005 en Indiana Univ. Math. J. 24 (1975) 87 - 91 state-of-the-art mathematics http://iumj.org/access/