An Approximate Morse-Sard Theorem James EellsJohn McAlpin Indiana University Mathematics Journal 1968 text pdf 10.1512/iumj.1968.17.17064 10.1512/iumj.1968.17.17064 en Indiana Univ. Math. J. 17 (1968) 1055 - 1064 state-of-the-art mathematics http://iumj.org/access/