If witnesses testified in January but were later exposed as false witnesses in July, then what happens to their unrelated testimony given in March? Abaye says that they are disqualified retroactively since they are evildoers. Rava says that the law of false witnesses is such a novelty that it cannot be analyzed logically; they are false only from now on, and their March testimony is unaffected.
This is the "A" in the six cases abbreviated Y A L K G M, where the law follows Abaye against Rava.
If a witness eats non-kosher meat because it is cheaper, he cannot testify because he can be bribed. What if he eats it to make a point? Abaye says that he is an evildoer, thus, disqualified. Rava says that for disqualification, he needs to be an evildoer in money matters, not ritual.
This is the "M" in the six cases abbreviated Y A L K G M, where the law follows Abaye against Rava.
Art: Gossip by Thomas Sully