Image of Subset under Mapping equals Union of Images of Elements
Jump to navigation
Jump to search
Theorem
Let $S$ and $T$ be sets.
Let $f: S \to T$ be a mapping from $S$ to $T$.
Let $X \subseteq S$ be a subset of $S$.
Then:
- $\ds f \sqbrk X = \bigcup_{x \mathop \in X} \map f x$
where:
- $f \sqbrk X$ is the image of the subset $X$ under $f$
- $\map f x$ is the image of the element $x$ under $f$.
Proof
By definition, a mapping is a relation.
Thus Image of Subset under Relation equals Union of Images of Elements applies.
$\blacksquare$
Sources
- 1971: Robert H. Kasriel: Undergraduate Topology ... (previous) ... (next): $\S 1.10$: Functions: Remark $10.8 \ \text{(d)}$