Commutative Subspace Lattices Kenneth Davidson Indiana University Mathematics Journal 1978 text pdf 10.1512/iumj.1978.27.27032 10.1512/iumj.1978.27.27032 en Indiana Univ. Math. J. 27 (1978) 479 - 490 state-of-the-art mathematics http://iumj.org/access/