Differentiable Maps with Small Critical Set or Critical Set Image P. ChurchJ. Timourian Indiana University Mathematics Journal 1978 text pdf 10.1512/iumj.1978.27.27064 10.1512/iumj.1978.27.27064 en Indiana Univ. Math. J. 27 (1978) 953 - 971 state-of-the-art mathematics http://iumj.org/access/