The end of the fourteenth chapter of mishnayos Y’vamos go through cases of two brothers’ marriages. The first cases are where both brothers, or both their wives, are deaf-mutes. Then come the following cases, in this order:
- one brother is a deaf-mute and neither wife is, and the wives are sisters
- one wife is a deaf-mute and neither husband is, and the wives are sisters
- one brother and his wife are deaf-mutes, and the other wife is her sister and not a deaf-mute
- one brother is a deaf-mute and neither wife is, and the wives are not sisters
- one wife is a deaf-mute and neither husband is, and the wives are not sisters
- one brother and his wife are deaf-mutes, and the other wife is not her sister and not a deaf-mute
Why doesn’t it also have the cases that one brother and the other’s wife are deaf-mutes (and the wives are sisters, or are not sisters)? That seems to be the one missing case.