The symmetric difference of $A$ and $B$ is the set $A\mathbin {\triangle }B$ defined by
\[ A\mathbin {\triangle }B \mathrel {\smash {\overset {\mathclap {\scriptscriptstyle \text{def}}}=}}\webleft (A\setminus B\webright )\cup \webleft (B\setminus A\webright ). \]
