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

List all the elements of the following set:
$D = \{ x : x \text{ is a letter in the word } \text{"LOYAL"} \}$

If $Q = \{x : x = \frac{1}{y}, y \in N\}$,then which of the following is true?

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 $x \notin A$.

Which of the following is an example of the null set?
$\{ x : x \in \mathbb{N}, x < 5 \text{ and } x > 7 \}$

Determine whether the following set is finite or infinite:
$\{1, 2, 3, \ldots, 99, 100\}$