How are proofs formatted when the answer is a counterexample? Suppose it is asked:

Prove or find a counterexample: the sum of two integers is odd

The fact that 1 + 1 = 2 is a counterexample that disproves that statement. What is the proper format in which to write this? I will provide my attempt.

Theorem: the sum of two integers is odd
Proof:
1 + 1 = 2
=> the sum of two integers may be even

I understand the math, but I'm not sure how to properly present a counterexample relative to an initial theorem. Was this an acceptable presentation of a proof?

Cite the counterexample.  Since $1 + 1 = 2$, the sum of two arbitrary integers is not always odd.
