Gittin 71B

והתנן: שני אחין חרשין ⁠– נשואין שתי אחיות פיקחות, או שתי אחיות חרשות, או שתי אחיות אחת פיקחת ואחת חרשת; וכן שתי אחיות חרשות ⁠– נשואות לשני אחין פיקחין, או לשני אחין חרשין, או לשני אחין אחד פיקח ואחד חרש ⁠– הרי אלו פטורות מן החליצה ומן היבום.

But didn’t we learn in a Mishnah (Yevamot 112b): In a case where there were two deaf-mute brothers, whose marriage is valid by rabbinic law, married to two halakhically competent sisters, or to two deaf-mute sisters, or to two sisters, one of whom was halakhically competent and one of whom was a deaf-mute; and similarly, if there were two deaf-mute sisters, whose marriage is valid by rabbinic law, married to two halakhically competent brothers, or to two deaf-mute brothers, or to two brothers, one of whom was halakhically competent and one of whom was a deaf-mute; and in each case one brother dies without children, then all these women are exempt from ḥalitza and from levirate marriage. Each sister is exempt, as she is the sister of the wife of the yavam.

ואם היו נכריות, יכנסו; ואם רצו להוציאן ⁠– יוציאו.

And if they were unrelated women the men may marry them in levirate marriage, and if they wanted to divorce them later via a bill of divorce they may divorce them. Since this is stated as a general halakha it indicates that the deaf-mute brother can also give a bill of divorce to his yevama who was previously married to his deaf-mute brother, and the rabbis did not institute a decree in order not to create confusion with the similar case of a deceased halakhically competent brother.

אלא מחוורתא כדשנין מעיקרא.

Rather, it is clear as we initially answered, that it is referring to a yevama, previously married to a halakhically competent brother, who fell before a yavam who was a deaf-mute from birth. The alternative answer given on the previous amud is rejected.