Connected Sums of Aspherical Manifolds Darryl McCullough Indiana University Mathematics Journal 1981 text pdf 10.1512/iumj.1981.30.30002 10.1512/iumj.1981.30.30002 en Indiana Univ. Math. J. 30 (1981) 17 - 28 state-of-the-art mathematics http://iumj.org/access/