# Category:Open Balls

This category contains results about open $\epsilon$-balls in the context of Metric Spaces.
Definitions specific to this category can be found in Definitions/Open Balls.

Let $M = \struct {A, d}$ be a metric space or pseudometric space.

Let $a \in A$.

Let $\epsilon \in \R_{>0}$ be a strictly positive real number.

The open $\epsilon$-ball of $a$ in $M$ is defined as:

$\map {B_\epsilon} a := \set {x \in A: \map d {x, a} < \epsilon}$

If it is necessary to show the metric or pseudometric itself, then the notation $\map {B_\epsilon} {a; d}$ can be used.

## Subcategories

This category has the following 4 subcategories, out of 4 total.