Universal Set
Universal set
In any discussion in set theory, there always happens to be a set that contains all sets under consideration i.e. it is a super set of each of the given sets. Such a set is called the universal set and is denoted by U. Thus a set that contains all sets in a given context is called the universal set.
Example
When we are using sets containing natural numbers, then N is the universal set.
Example
If A = {1, 2, 3} B = { 2, 4, 5, 6 } and C { 1, 3, 5, 7} , then U = {1, 2, 3, 4, 5, 6, 7} can be taken as the universal set.
Example
When we are using intervals on real line, the set R of real numbers is taken as the universal set.