Commuting Observables in a \sigma-Orthologic Barbara Jeffcott Indiana University Mathematics Journal 1974 text pdf 10.1512/iumj.1974.23.23030 10.1512/iumj.1974.23.23030 en Indiana Univ. Math. J. 23 (1974) 369 - 376 state-of-the-art mathematics http://iumj.org/access/