Definition:Continuity/Metric Subspace
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Definition
Let $M_1 = \left({A_1, d_1}\right)$ and $M_2 = \left({A_2, d_2}\right)$ be metric spaces.
Let $f: A_1 \to A_2$ be a mapping from $A_1$ to $A_2$.
Let $Y \subseteq A_1$.
By definition, $\left({Y, d_Y}\right)$ is a metric subspace of $A_1$.
Let $a \in Y$ be a point in $Y$.
Then $f$ is $\left({d_Y, d_2}\right)$-continuous at $a$ if and only if:
- $\forall \epsilon > 0: \exists \delta > 0: d_Y \left({x, a}\right) < \delta \implies d_2 \left({f \left({x}\right), f \left({a}\right)}\right) < \epsilon$
Similarly, $f$ is $\left({d_Y, d_2}\right)$-continuous if and only if:
- $\forall a \in Y: f$ is $\left({d_Y, d_2}\right)$-continuous at $a$
Also see
Sources
- 1975: W.A. Sutherland: Introduction to Metric and Topological Spaces ... (previous) ... (next): $2.2$: Examples: Example $2.2.5$