Definition:Lower Level Set

Definition
Let $f: S \to \overline \R$ be an extended real-valued function.

Let $\alpha \in \R$.

The $\alpha$-lower level set of $f$ is the set:


 * $\ds \operatorname {lev} \limits_{\mathop \le \alpha} f := \set {x \in S: \map f x \le \alpha}$

Also see

 * Definition:Lower Closure