Singularly Fibered Homotopy Spheres Ronald FintushelJ. Walsh Indiana University Mathematics Journal 1981 text pdf 10.1512/iumj.1981.30.30015 10.1512/iumj.1981.30.30015 en Indiana Univ. Math. J. 30 (1981) 179 - 192 state-of-the-art mathematics http://iumj.org/access/