The Homology Groups of a Lattice J. Folkman Indiana University Mathematics Journal 1966 text pdf 10.1512/iumj.1966.15.15043 10.1512/iumj.1966.15.15043 en Indiana Univ. Math. J. 15 (1966) 631 - 636 state-of-the-art mathematics http://iumj.org/access/