Preimage of Singleton

Theorem
Let $\mathcal R$ be a relation.

Let $\mathcal R^{-1} \left({t}\right)$ denote the preimage of $t$ under $\mathcal R$.

Let $\mathcal R^{-1} \left({ \left\{{t}\right\} }\right)$ denote the preimage of $\left\{{t}\right\}$ under $\mathcal R$.

Then:
 * $\mathcal R^{-1} \left({ \left\{{t}\right\} }\right) = \mathcal R^{-1} \left({t}\right)$