کدام گزینه درست نیست؟
1 )
$\mathbb{Q} = \left\{ {\frac{a}{b}\left| {a \in \mathbb{Z},b \in \mathbb{N}} \right.} \right\}$
2 )
$A - B = \left\{ {x\left| {x \in A,x \notin B} \right.} \right\}$
$A \cup B = \left\{ {x\left| {x \in A و x \in B} \right.} \right\}$
4 )
$A \cap B = \left\{ {x\left| {x \in Aوx \in B} \right.} \right\}$