1. A pole that was not used as a valid Lechi before Shabbos cannot become one on Shabbos.
2. There is a dispute about the Halachah in the case of a pole that was originally built as part of the Mavoy, which people now (before Shabbos) want to consider as the Lechi to the Mavoy to permit carrying in the Mavoy.
3. The Gemara proves that the law of a wall serving as a partition differs from the law of a pole serving as a Lechi in this regard (#2).
4. Based on the difference between walls and poles (#2-3), the Gemara explains the argument between Abaye and Rava (#2).
5. There is a dispute about whether one may use a living creature as a Lechi.
Sounds like Pharaoh putting the babies into the wall – please clarify
A BIT MORE
1. If a designated Lechi fell down and there happened to be another pole at the entrance to the Mavoy that fit the criteria of a Lechi, everyone agrees that this pole does not permit carrying in the Mavoy. A pole must be designated as a Lechi before Shabbos.
2. Abaye: This is a valid Lechi. Rava: Since the pole was not built with intent that it serve as a Lechi, it is not considered a Lechi until it is made expressly for this purpose.
3. If a wall was standing before Shabbos, it helps transform an area into a Reshus ha'Yachid even if nobody considered using the wall for this purpose before Shabbos.
4. Abaye says that a Lechi does not need to be made for the purpose of permitting a Mavoy since it serves as a wall, and walls do not have to be made for the specific purpose of creating a Reshus ha'Yachid. Rava says that the Lechi serves merely as a reminder, and as such it must be made for this specific purpose (for otherwise it is not a reminder).
5. The Tana Kama: It is permitted. Rebbi Meir: It is prohibited.