A Theorem on Two Commuting Observables Arlan Ramsay Indiana University Mathematics Journal 1966 text pdf 10.1512/iumj.1966.15.15017 10.1512/iumj.1966.15.15017 en Indiana Univ. Math. J. 15 (1966) 227 - 234 state-of-the-art mathematics http://iumj.org/access/