Yevamot 3B

למעוטי דרב ודרב אסי. לרב ולרב אסי למעוטי מאי?

The Talmud answers that these enumerations come to exclude those additions of Rav and of Rav Asi. Rav added the rival wife of a woman suspected by her husband of adultery [sota], while Rav Asi added the rival wife of an aylonit. The Talmud asks: And according to the opinion of Rav and according to the opinion of Rav Asi, the enumeration of the Mishnah comes to exclude what?

אי סבירא להו דהדדי ⁠— חדא למעוטי צרת ממאנת, וחדא למעוטי צרת מחזיר גרושתו.

The Talmud responds: If each maintains in accordance with the opinion of the other, then one enumeration of the Mishnah comes to exclude the rival wife of a wife who performed refusal. If the deceased brother had two wives, one of whom was a minor, and she refused the yavam, her rival wife is prohibited from levirate marriage with him. However, the latter is not entirely exempt and must perform ḥalitza. And the other one comes to exclude the rival wife of the wife of one who remarries his divorcée, i.e., a woman who was illicitly remarried by her former husband after she had been married to another man.

ואי לא סבירא להו דהדדי ⁠— חדא למעוטי דחבריה, וחדא למעוטי או צרת ממאנת, או צרת מחזיר גרושתו.

And if Rav and Rav Asi do not each maintain in accordance with the opinion of the other, then one enumeration comes to exclude the opinion of the other, as they do not agree that the halakha stated by the other should be included in the Mishnah, and the other one comes to exclude one of the above suggestions, either the rival wife of a wife who performed refusal or the rival wife of the wife of one who remarries his divorcée.