# Definition:Limit of Mapping between Metric Spaces/Epsilon-Delta Condition

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## Definition

Let $M_1 = \struct {A_1, d_1}$ and $M_2 = \struct {A_2, d_2}$ be metric spaces.

Let $c$ be a limit point of $M_1$.

Let $f: A_1 \to A_2$ be a mapping from $A_1$ to $A_2$ defined everywhere on $A_1$ *except possibly* at $c$.

Let $L \in M_2$.

$\map f x$ is said to **tend to the limit $L$ as $x$ tends to $c$** and is written:

- $\map f x \to L$ as $x \to c$

or

- $\ds \lim_{x \mathop \to c} \map f x = L$

- $\forall \epsilon \in \R_{>0}: \exists \delta \in \R_{>0}: 0 < \map {d_1} {x, c} < \delta \implies \map {d_2} {\map f x, L} < \epsilon$

That is, for every real positive $\epsilon$ there exists a real positive $\delta$ such that *every* point in the domain of $f$ within $\delta$ of $c$ has an image within $\epsilon$ of some point $L$ in the codomain of $f$.

This is voiced:

**the limit of $\map f x$ as $x$ tends to $c$**.

## Also known as

**$\map f x$ tends to the limit $L$ as $x$ tends to $c$**

can also be voiced as:

**$\map f x$ approaches the limit $L$ as $x$ approaches $c$**