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Rebbi Yochanan says that most of the Jews living in the areas to which the ten tribes were exiled are Mamzerim. (1)
Shmuel says that a child born from a Nochri mother and a Jewish father is not Jewish.
Ravina says that a child born from a Nochri father and a Jewish mother is regarded as Jewish.
The girls of the generation of the exile of the Ten Tribes were unable to bear children.
Klal Yisrael will make a Yom Tov on the day that Tarmod is destroyed. (2)
People of uncertain lineage congregate in the city of Harfnaya, thus making it a city full of Mamzerim. (3)
Our Sages derive from the verse that a brother born after his older brother dies without children is prohibited to the Yevamah and to her Tzaros.
The Mitzvah of Yibum applies only to brothers from the father and not to brothers from the mother.
Our Sages derive from the word "Yachdav" that Yibum applies only to the wife of a brother and not to the wife of an uncle.
Our Sages derive from the Gezeirah Shavah of "Achim" that the Mitzvah of Yibum applies to all brothers from a father, and not only to brothers that share both a father and a mother. (4)
Rav Huna: If the Shomeres Yavam (a Yevamah prior to Yibum) dies, the Yavam is permitted to marry her mother even if he is the sole Yavam. Rav Yehudah: The mother is prohibited even after the death of the Shomeres Yavam. (5)
Even Rav Huna agrees that while the Shomeres Yavam is alive, her mother is prohibited because it is forbidden to annul the Mitzvah of Yibum. (6)
A BIT MORE
1. This opinion maintains that a child born from a Jewish mother and a Nochri father is a Mamzer.
2. This is because the residents of the city are Mamzerim and they marry into Klal Yisrael, creating more Mamzerim.
3. The city of Harfnaya is worse than Gehinom, because there is hope for the people who go to Gehinom but there is no hope for the Mamzerim of Harfnaya.
4. Since Yibum is a novel Mitzvah that permits an Ervah who is usually forbidden, one might have thought that it applies only to brothers who share both parents.
5. Rav Huna: The impending Mitzvah of Yibum does not bond the Yevamah to the Yavam -- "Ein Zikah." Rav Yehudah: The impending Mitzvah of Yibum bonds the Yevamah to the Yavam -- "Yesh Zikah."
6. If the Yavam would marry the mother, the Mitzvah of Yibum would no longer apply to the daughter.
BROTHERS FROM A FATHER SHARE AN INHERITANCE
The Gemara says that one might have thought that Yibum applies to the wife of an uncle. Therefore, the Sages derive from the word "Yachdav" that it applies only to brothers. Rashi explains that this verse refers to brothers who share the same inheritance, as opposed to Lot who does not share an inheritance (with Avraham). The Rashba asks that Lot does share the inheritance of his grandfather Terach together with Avraham. Additionally, brothers from the mother also share an inheritance upon the death of their mother. The Rashba answers that since Lot shares the inheritance only because his father already died, and had his father been alive he would not inherit, and brothers from the mother inherit their mother's property only when her husband predeceases her, it is not regarded as "Yachdav" since the inheritance is not a sure thing.
THE MITZVAH OF YIBUM
If a brother from the father dies without children, it is a Mitzvah to do Yibum with his wife, whether she is a wife from Eirusin or from Nisu'in. (Shulchan Aruch EH 156:1)
Even if his wife has children from a previous marriage, the Mitzvah of Yibum still applies. (Pischei Teshuvah)
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