of a function
The set of points in on which . If the function is given on a square of the plane and has partial derivatives there which also satisfy a Lipschitz condition, then for almost-all in the interval the level set
consists of a finite number of regular curves (on them, ). Cf. Sard theorem.
Level set. Encyclopedia of Mathematics. URL: http://www.encyclopediaofmath.org/index.php?title=Level_set&oldid=18462