This theorem states that if a and b are positive integers, then their sum a + b is also a positive integer. This is true because both a and b are positive, so their sum must be positive as well.
About this solution: The candidate's solution is correct and demonstrates a level of completeness. The candidate has correctly identified that this is a direct result of the definition of addition for integers. The candidate has also correctly identified that the sum of two integers will always be an integer. Therefore, the candidate's solution solves the problem and is a correct approach.