Definition:Closed Unit Ball

Definition
Let $\struct {X, \norm {\, \cdot \,}}$ be a normed vector space.

Let $a \in X$.

The closed unit ball of $X$, denoted $\operatorname{ball} X$, is the set:


 * $\map {B_1^-} a := \set {x \in X: \norm {x - a} \le 1}$