A set is a collection of well-defined objects.
The objects in the set are called elements.

If a set has no elements, then it is called the null set it the empty set.
It Is denoted by the symbol ø or { } .

If all the elements of a set A are also in a set B, then we say that A is a subset of B..

The universal set is the set that contains all elements.
Every set is a subset of the universal set.

The intersection