Integers are the numbers that are in either (1) the set of whole numbers, or (2) the set of numbers that contain the negatives of the natural numbers. If the set of integers is denoted by I, then

I = {......, -3, -2, -1, 0, 1, 2, 3, ......}

Positive integers are the numbers in I greater than 0. Negative numbers are the numbers in I less than 0.
The number zero is neither positive nor negative, i.e., it is both nonpositive and nonnegative.

Given the above definitions, the following statements about integers can be made:

(1) N is the set of positive integers.
(2) W is the union of N and the number 0.
(3) The set of numbers that contain the negatives of the numbers in N is
the set of negative integers.
(4) I is the union of W and the set of negative integers.