サードの定理
Sternberg, Shlomo (1964), Lectures on differential geometry, Englewood Cliffs, NJ: Prentice-Hall, pp. xv+390, MR0193578, Zbl 0129.13102 .
Morse, Anthony P. (January 1939), “The behaviour of a function on its critical set”, Annals of Mathematics 40 (1): 62–70, doi:10.2307/1968544, JSTOR 1968544, MR1503449, https://jstor.org/stable/1968544 .
Sard, Arthur (1942), “The measure of the critical values of differentiable maps”, Bulletin of the American Mathematical Society 48 (12): 883–890, doi:10.1090/S0002-9904-1942-07811-6, MR0007523, Zbl 0063.06720, http://www.ams.org/bull/1942-48-12/S0002-9904-1942-07811-6/home.html .