Image of Singleton under Relation

Theorem
Let $$\mathcal{R} \subseteq S \times T$$ be a relation.

Then the image of an element of $$S$$ is equal to the image of a singleton containing that element, the singleton being a subset of $$S$$:

$$\forall s \in S: \mathcal{R}\left({s}\right) = \mathcal{R}\left({\left\{{s}\right\}}\right)$$.