Yevamot, Chapter Thirteen, Mishnah Eight
Usually when two women are married to a man and he dies without children, when one of the brothers performs yibbum or halitzah with one of the widows, the other is automatically exempt. Yibbum or halitzah are not performed for each wife. Our mishnah discusses situations in which at least one of the marriage was only derabbanan either because she was a minor or a deaf-mute. The general rule in such cases is that yibbum or halitzah with a wife whose marriage was only derabbanan does not exempt a wife whose marriage was deoraita. However, yibbum or halitzah with a wife whose marriage is deoraita does exempt a wife whose marriage was derabbanan. Furthermore, yibbum or halitzah with a wife whose marriage was derabbanan exempts another wife whose marriage was derabbanan, as long as both marriages were of the exact same status.
1) If a man who was married to two minors orphans died, intercourse or halitzah with one of them exempts her rival.
2) And the same is true with regard to two deaf women.
3) [If a man was married to] a minor and to a deaf woman [and then died], intercourse with one of them does not exempt her rival.
4) If one was of sound senses and one was deaf, intercourse with the woman of sound senses exempts the deaf woman, but intercourse with the deaf woman does not exempt the woman of sound senses.
5) If one was of age and the other a minor, intercourse with the one of age exempts the minor, but intercourse with the minor does not exempt the one of age.
Section one: In this section both marriages were derabbanan; therefore intercourse (yibbum) or halitzah by the yavam with one of the widows exempts the other one. Note that some commentators hold that the minor can perform halitzah only when she reaches majority age. Others hold that she may even do so as a minor (see above 12:4).
Section two: Again both marriages are derabbanan therefore yibbum with one wife exempts the other. Note that in this case yibbum is the only option because as we learned in 12:4, a deaf-mute woman cannot perform halitzah.
Section three: In this case, both marriages were derabbanan, but one was with a deaf-mute and one was with a minor. Since we dont know who is more married, both require halitzah or yibbum. The minor may be more married because her marriage will be completed upon reaching majority age. On the other hand the deaf-mute may be more married because she is more capable of having intercourse.
Section four: In this case, one wife was of sound sensesshe was not a deaf-mute or insaneand the other wife was a deaf-mute. Since the marriage with the former was of deoraita status, yibbum or halitzah with her exempts the latter. However, since the latters marriage was of derabbanan status, yibbum with her does not exempt the former.
Section five: This section teaches the same rule as in the previous section; it just uses the example of a minor and a girl of majority age.