Modifications and Cobounding Manifolds II Andrew Wallace Indiana University Mathematics Journal 1961 text pdf 10.1512/iumj.1961.10.10054 10.1512/iumj.1961.10.10054 en Indiana Univ. Math. J. 10 (1961) 773 - 809 state-of-the-art mathematics http://iumj.org/access/