Is the output produced a valid answer the the question asked? If the answer is yes then there is no problem is there? That the answer you get is correct is guaranteed and violation of this is a bug. If there are multiple correct answers to the question you posed then you may get back any one of them, and which one in particular is undefined. The only way to ensure that you only get *one* specific correct answer is to make sure that the question is framed such that there can only be that one correct answer.