### Theory:

Let us recall the definition of sets.
A set is a collection of the well-defined object.
Set notation: A set is denoted by capital letters English alphabets $$A, B, C, D,...$$

Elements: Elements of the sets are denoted by small letters English alphabets $$a, b, c,...$$
Also, the elements of the set should be written inside the curly brackets $\left\{\right\}$.
Types of sets.
There are many types of sets in set theory. They are:
1. Empty set
2. Singleton set
3. Finite set
4. Infinite set
5. Equivalent sets
6. Equal sets
7. Subsets
8. Proper set
9. Power set