Even Integer Plus 5 is Odd/Historical Note

Historical Note on Even Integer Plus 5 is Odd
There is nothing profound about this result.

used it as a simple demonstration of the construction of various kinds of proof in his of $1977$.

It is questionable whether the indirect proof and the Proof by Contradiction actually constitute different proofs of this result, but both are included on anyway, in case they are found to be instructional.

He sets a similar theorem as an exercise:
 * Prove the implication "If $x$ is an odd integer, then $y = x - 3$ is an even integer" using the three proof techniques: ...

but it has been considered not sufficiently different from this one to be actually included on as a separate result to be proved.

For similar reasons, several other trivial exercises in applied logic have also been omitted from this site.