Question

Check whether the sets $A$ and $B$ are disjoint:
$A=\{1,2,3\}$ and $B=\{4,5,\{1,2,3\}\}$

Answer 1

$A=\{1,2,3\}$

$B=\{4,5\{1,2,3\left\}\right\}$

$A\cap B=\{1,2,3\}$

So , A and B are not disjoint.