Cardinality of Set of All Mappings/Infinite Sets

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Theorem

Let $S$ and $T$ be sets such that either $S$ or $T$ is infinite.

The cardinality of the set of all mappings from $S$ to $T$ (that is, the total number of mappings from $S$ to $T$) is:

$\card {T^S} = \card T^{\card S}$


Proof