Let $X$ be a D11: Set such that

(i)	${\sim} \subseteq X \times X$ is an D178: Equivalence relation on $X$
(ii)	\begin{equation} \forall \, x \in X : [x]_{\sim} : = \{ y : (x, y) \in {\sim} \} \end{equation}

The quotient set of $X$ modulo ${\sim}$ is the D11: Set \begin{equation} X / {\sim} : = \{ [x]_{\sim} : x \in X \} \end{equation}