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

What universal set $(U)$ would you propose for each of the following:
The set of isosceles triangles

With reference to a universal set,the inclusion relation $(\subseteq)$ of a subset in another is:

Let $x_{1}, x_{2}, \ldots, x_{15}$ be $15$ distinct numbers chosen from $1, 2, 3, \ldots, 15$. Then, the value of $(x_{1}-1)(x_{2}-1)(x_{3}-1) \ldots (x_{15}-1)$ is

Which of the following is an example of the null set?
$\{ y : y \text{ is a point common to any two parallel lines} \}$

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