The symmetric difference of $U$ and $V$ is the set $U\mathbin {\triangle }V$ defined by1
\[ U\mathbin {\triangle }V \mathrel {\smash {\overset {\mathclap {\scriptscriptstyle \text{def}}}=}}\webleft (U\setminus V\webright )\cup \webleft (V\setminus U\webright ). \]
1Illustration:
