brought to you by Kollel Iyun Hadaf of Yerushalayim
& Revach l'Neshamah - http://www.revach.net
1. If a Korah (beam) is placed more than 20 Amos above the ground in a Mavoy (alleyway), it must be lowered in order to permit carrying in the Mavoy.
2. An Eruv permits carrying in a Chatzer or Mavoy only when the width of the Mavoy' s entranceway is less than 10 Amos.
3. The Gemara explains why the Mishnah in Sukah says that a 20-Amah-high Sukah is invalid, while the Mishnah here says that a 20-Amah-high Korah should be lowered.
4. The Mishkan is also called a "Mikdash," and the Mikdash is also called a "Mishkan."
5. Rebbi Yehudah says that a Korah may be placed more than 20 Amos above the ground in an alleyway.
A BIT MORE
1. If a Korah is placed over the entrance of a Mavoy that has three walls (one in the back and two on the sides), it is permissible to carry in the Mavoy on Shabbos, since it is now considered a Reshus ha'Yachid, a private domain. However, it is permissible to carry only if the Korah is less than 20 Amos above the ground.
2. An entranceway is defined as an opening less than 10 Amos wide. If it is 10 Amos or more, it is not considered an entranceway ("Pesach") but a breach in the partition which disrupts its status of being of a Reshus ha'Yachid. However, if there is a Tzuras ha'Pesach above the entranceway, then it may be more than 10 Amos wide.
3. One explanation is that the laws of how high that Sechach must be are Torah laws, and it is not necessary for the Mishnah to teach how to correct a Sukah that was built in the wrong way. In contrast, the laws of Eruvin are mid'Rabanan and the details are known only through the Mishnah. The Mishnah therefore teaches how to correct the placement of a Korah.
4. For example, when the Torah teaches that a Beis ha'Mikdash will be built in Eretz Yisrael, it calls it a "Mishkan" (Vayikra 26:11).
5. The Gemara discusses whether Rebbi Yehudah's statement in the Beraisa, "It is valid until 40 or 50 Amos," means only up to 50 or that there is no maximum height.
Next Daf Index to Revach for Maseches Eruvin