V. SET TYPES

1. The Finite sets, which sets has the number of members is limited (finite).
          For example:
                    A = {1, 3, 5, 7}, set A is finite set because n (A) = 5.

2. The Infinite sets, namely that the number of members is infinity (infinite).
           For example:
             A = {1, 2, 3, 4,. . . }, Set A is infinite set because n (A) = infinity.

3. The Empty set (empty set or void or NULL set), is set that does not contain anything that element.
For example:
         B = {four-legged chickens}, and
         C = {x | x < 7, divisible by 9, x natural numbers}.
It is clear that there is no chicken-legged 4 and obviously also no natural numbers which satisfy the required conditions on the set C. Therefore, set B and C above do not contain elements and said something that set B and C is the set of "empty".

Empty set is written with the symbol ∅ or { }.
So B = ∅ or B = { } and C = ∅ or C = { }