Final Cover - For Printing

20. Singleton Set
    A set with only one element is said to be a singleton set.

Eg. : B = {4}

Here, n(B) = 1, and hence B is a singleton set.

21. Union of Sets
    If A and B are any two sets, then their union denoted as A^ ∪^ B, is the set of elements
    belonging either to A, or to B, or to both.

Eg. : If A = {1, 2, 3} and

B = {3, 4, 5}

Then, A∪B = {1, 2, 3, 4, 5}

Note that even though one particular element, namely 3, appears in both the sets, in

the union set it has to be written only once. In general, a set should never contain an

element more than once. In other words, a set should contain well defined distinct

objects only.

A number of concepts can be taught by using the fingers of the hand. Take a particular

hand for demonstration. Consider the union of two sets with the fingers as the sets,

say for instance, {little finger, ring finger, middle finger} and {little finger, index

finger, thumb} as two different sets. The union of these two sets is the set with all

the five fingers of the hand. Note that the hand is not having two little fingers and

hence the union set will contain only one little finger, even though it is repeated in

both the sets.

The ideas of intersection, complementation and difference can also be taught using
the fingers of the hand.