Sets: Terminologies, Notations, and Operations

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 U.

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


If sets A and B have elements in common they form a set written as A \cap B. This is the intersection of A and B.

Intersection of Sets

Example: If we let A = \{1, 2, 3, 4, 5\} and B = \{2, 4, 6\} then A \cap B = \{2,4\}. » Read more