On the Obstruction P(F, f) to the Product Theorems of Fiber-Preserving Maps Soon-Kyu KimDennis McGavranJingyal Pak Indiana University Mathematics Journal 1976 text pdf 10.1512/iumj.1976.25.25057 10.1512/iumj.1976.25.25057 en Indiana Univ. Math. J. 25 (1976) 725 - 732 state-of-the-art mathematics http://iumj.org/access/