Let $X$ and $Y$ each be a D11: Set.
The difference of $X$ and $Y$ is the D11: Set \begin{equation} X \setminus Y : = \{ x \in X : x \not\in Y \} \end{equation}

Let $X$ and $Y$ each be a D11: Set.
The difference of $X$ and $Y$ is the D11: Set \begin{equation} X \setminus Y : = \{ x : x \in X \text{ and } x \not\in Y \} \end{equation}