Which of the following is not a Peanos postulate?
1
\(\mathbb N\) is empty.
2
Associated with each natural number n there is a unique natural no. n' called the successor of
3
There is a natural no. n that is not the successor of any natural no.
4
The only subset of \(\mathbb N\) that contains x̅ and the successors of all its elements is \(\mathbb N\) itself