Who is the author of the poem disputed by two individuals, each of whom swore by the Qur'an that it belongs to him, while one of them claims it belongs to a deceased poet?

The correct position is that of the one who attributed the poem to himself, because he is affirming and informing about himself. As for the one who attributed it to someone else, he is negating and informing about someone else, and his statement is not accepted except with valid evidence.