Self-Intersections of Immersed Manifolds R. LashofS. Smale Indiana University Mathematics Journal 1959 text pdf 10.1512/iumj.1959.8.58010 10.1512/iumj.1959.8.58010 en Indiana Univ. Math. J. 8 (1959) 143 - 157 state-of-the-art mathematics http://iumj.org/access/