The set $A = \{ x : x \ne x \}$ represents:

Are the following pair of sets equal? Give reasons.
$A = \{ 2, 3 \}, \quad B = \{ x : x \text{ is a solution of } x^2 + 5x + 6 = 0 \}$

If ${N_a} = \{an : n \in N\}$,then ${N_5} \cap {N_7} = $

Write the following interval in set-builder form: $\left[ -23, 5 \right)$

In each of the following,determine whether the statement is true or false. If it is true,prove it. If it is false,give an example.
If $A \subset B$ and $x \notin B,$ then $x \notin A$.

Let $A = \{1, 2, 3, 4, 5, 6\}$. Insert the appropriate symbol $\in$ or $\notin$ in the blank space:
$5 \dots A$