Duality in the Cohomology Ring of Transitive Permutation Representations Ernst Snapper Indiana University Mathematics Journal 1965 text pdf 10.1512/iumj.1965.14.14023 10.1512/iumj.1965.14.14023 en Indiana Univ. Math. J. 14 (1965) 323 - 336 state-of-the-art mathematics http://iumj.org/access/