As a preparation for more posts on probability, statistics, permutations and combinations, we familiarized ourselves last week with the different terminologies and notations of probability. We continue in this post by studying set terminologies, notations, and operations. Note that this is also the third post in the **Set Primer Series;** the first and second are Introduction to Sets and Subset: a set contained in a set.

**Universal Set**

The *universal set* is the set that contains all the elements under discussion. If we talk about the letters in the English alphabet, then the universal set contains all the 26 letters. In set theory, universal set is usually denoted by .

In the following discussion, we let be the set of integers, be the set of even integers, and be the set of odd integers. The following are the common operations on sets.

**Intersection**

If sets and have elements in common they form a set written as . This is the *intersection* of and .

Example: If we let and then . » Read more