Set of All Mappings is Small Class
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Theorem
Let $S$ and $T$ be small classes.
It follows that the set of all mappings $S^T$ is a small class.
Proof
The set of all mappings $S^T$ is equal to the collection of all mappings $f : S \to T$.
Each of these mappings $f$ is a subset of $S \times T$.
Thus, $S^T \subseteq \powerset {S \times T}$.
Therefore, by Cartesian Product is Small and the axiom of powers, $S^T$ is a small class.
$\blacksquare$
Sources
- 1971: Gaisi Takeuti and Wilson M. Zaring: Introduction to Axiomatic Set Theory: $\S 10.48$