Von Neumann's inequality for commuting weighted shifts Michael Hartz Indiana University Mathematics Journal 2017 text pdf 10.1512/iumj.2017.66.6074 10.1512/iumj.2017.66.6074 en Indiana Univ. Math. J. 66 (2017) 1065 - 1079 state-of-the-art mathematics http://iumj.org/access/