The following definitions will be used in the proof of the statement.

An integer n is even if, and only if, n equals twice some integer. An integer n is odd if, and only if, n equals twice some integer plus 1. Symbolically, for any integer, n
n is even ⇔ n = 2k for some integer k
n is odd ⇔ n = 2k + 1 for some integer k
Prove the following statement.
The difference of any two odd integers is even.