The set of integers between -5.1 and 2.1. The set containing all animals that have pouches to carry their young. The set consisting of natural numbers less than 20 and divisible by 3. A is the set of natural numbers that are multiples of 5. C is the set of all countries located on the Australian continent.
P is called a subset of set Q if all the elements of P are also elements of Q .
The fact that equality is included in the above definition can sometimes be inconvenient. By convention, it is represented in a Venn diagram as the outer boundary containing all the elements of interest. There is no prescribed shape for this boundary however a rectangle is frequently used for convenience. A is the set of all those elements of the universal set which are not in A . It is the shaded area in Figure 4.3.