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1. The Gemara explains that these guidelines (Daf 46, #4-5) apply only when we have no later ruling to the contrary.
2. The Gemara entertains the possibility that these rules are not unanimously accepted.
3. Rav Nachman says that we rule in accordance with Rebbi Meir when he makes decrees.
4. A person might not be able to learn Torah from every person who teaches Torah.
5. These rules (Daf 46, #4-5) apply not only to Mishnayos, but also to Beraisos.
A BIT MORE
1. For example, if an Amora says that we rule according to Rebbi Shimon in a certain case where he argues with Rebbi Yehudah, this does not contradict the rule that the Halachah follows Rebbi Yehudah. The rule states merely that in lieu of an Amora stating otherwise, the Halachah follows the view of Rebbi Yehudah.
2. When the Gemara questions these rules from a statement made by Rav, it answers that it is possible that Rav does not agree with these rules. The Gemara concludes that Rav Mesharshiya indeed does not agree with these rules, and he understands that Rav does not agree with them either.
3. Even though the Gemara earlier that we almost never rule according to Rebbi Meir when he argues with others (such as with Rebbi Yehudah or Rebbi Yosi), the Halachah does follow his view with regard to decrees that he established.
4. Rebbi Yosi says that a Kohen may travel over an area which causes Tum'ah d'Rabanan (of Tum'as Mes) in order to learn Torah from a teacher from whom he wants to learn, despite the fact that there are teachers in his area from whom he could learn. The fact that he does not want to learn from them indicates the likelihood that he will not learn well from them. The Mitzvah to learn Torah overrides the prohibition of Tum'ah d'Rabanan.
5. Abaye explains that this is evident from the fact that Rebbi Yochanan had to say that the Halachah follows Rebbi Yosi, even though this is seemingly evident from the other guidelines. It must be that Rebbi Yochanan's intention was to teach that these rules apply to disputes in Beraisos as well.
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