CONCERN LEST A WALL BE DIMINISHED
Questions: Originally, we thought that Rav and Shmuel argue when they made an Eruv together (Rav forbids due to the breach), and when they did not (Rav permits when there is no breach). How did we understand these two arguments?
Answer - part 1: When they did not make an Eruv together, they argue about [a Lechi that is] visible from the outside [of the Mavoy], but not from the inside;
Answer - part 2: When they made an Eruv together, they argue about Rav Yosef's law:
(Rav Yosef): The Mavoy is permitted only if it opens into the middle of [the wall of] the Rechavah. If it opens to the side (the end of the wall) it is forbidden. (It looks like an extension of the Mavoy opens to Reshus ha'Rabim, i.e. it is Mefulash. See Perush Chai diagram, Perek 1 number 73 in the English Charts section.)
(Rabah): [Even] when the Mavoy opens to the middle of the Rechavah, it is permitted only if the two breaches of the Rechavah are not directly opposite each other. If they are, it is forbidden (it appears to be Mefulash);
(Rav Mesharshiya): [Even] when the breaches of the Rechavah are not directly opposite each other, it is permitted only regarding a joint Rechavah. If it opens to a private Rechavah it is forbidden, lest the owner build houses [where the Rechavah is wider than the Mavoy], and the Mavoy will then be open to the side of the Rechavah, which is forbidden.
Question: What is the source to distinguish a joint Rechavah from a private one?
Answer: Ravin bar Rav Ada taught that there was a Mavoy, in which one end (Rashi's text - side 'wall') was the sea (the shore declined 10 Tefachim, and it was steep enough to be considered a wall), and the other end [or side wall] was a wasteheap [10 Tefachim tall. See Perush Chai diagrams, Perek 1 numbers 77,78 in the English Charts section.] Rebbi did not permit or forbid;
He did not forbid, for it has walls. He did not permit, lest part of the wasteheap be removed [and less than 10 remain] or the sea deposit debris (extending the shore, so it would no longer count as a wall).
Question: We are not concerned lest a wasteheap be removed!
(Mishnah): If a wasteheap in Reshus ha'Rabim is 10 Tefachim tall, one may throw to it from a window above. (The object goes through Makom Patur. It is always above 10. We are not concerned lest the wasteheap be removed [or reduced to less than 10 tall], and he throws four Amos through Reshus ha'Rabim. See note 2 in Appendix.)
Answer: We must say that the Mishnah discusses a joint wasteheap. (We are not concerned lest it be removed.) Rebbi was concerned for a private wasteheap.
Likewise, we distinguish a joint Rechavah from a private one!
Question: What did other Chachamim say [about the Mavoy between the sea and wasteheap]?
Version #1 - Answer (R. Yosef bar Avdimi - Beraisa): Chachamim forbid.
(Rav Nachman): The Halachah follows Chachamim.
Version #2 - Answer (R. Yosef bar Avdimi - Beraisa): Chachamim permit.
(Rav Nachman): The Halachah does not follow Chachamim.
(In Sura, many Mavo'os were open to the sea on one end.) Mereimar [did not rely on the sea to be a wall, rather, he] made nets for the openings, lest the sea deposit debris.
There was a bent Mavoy in Sura. A mattress was rolled up and put at the bend [and a Lechi was set up at only one end of the Mavoy].
(Rav Chisda): This is not like Rav or Shmuel!
Rav considers it a Mavoy Mefulash. He requires Tzuras ha'Pesach;
Shmuel says that it suffices to have a Lechi at each end (some say - and in the middle), but proper Lechayayim are needed. A wind can knock down a mattress! (Therefore, even the end of the Mavoy with a Lechi is forbidden. Ran - Shmuel considers the bend as if it was sealed, so nothing is needed there! Rather, the text should say that the mattress was put at an end of the Mavoy.]
The mattress counts as a Lechi [and permits, according to Shmuel] if it is pinned and attached [to the wall].
A BREACHED MAVOY
(R. Yirmeyah bar Aba citing Rav): If a Mavoy was totally breached to a Chatzer, and also the opposite wall of the Chatzer was also breached, the Chatzer is permitted, but the Mavoy is forbidden.
Question (Rabah bar Ula): We already learn this from a Mishnah!
(Mishnah): If a small Chatzer was breached to a big Chatzer, the big Chatzer is permitted, the small Chatzer is forbidden, for it is like an opening of the big one [but not vice-versa].
Answer (Rav Bivi bar Abaye): Perhaps the Mishnah permits only because Rabim do not pass through. Here, Rabim pass through. (The Mavoy and Chatzer are open to Reshuyos ha'Rabim on opposite sides.) One might have thought that even the Chatzer is forbidden. Rav teaches that this is not so.
Question (Rabah bar Ula): We know this from a Beraisa!
(Beraisa): If Rabim enter through one side of a Chatzer and leave through another side, it is a Reshus ha'Rabim regarding [being lenient about Safek] Tum'ah. It is a Reshus ha'Yachid regarding Shabbos.
Answer #1 (Rav Bivi): One might have thought that the Beraisa permits only if the openings are not opposite each other, but if they were, it would be forbidden (Rav teaches that this is not so.)
Question: Rabah forbids if the openings are opposite each other. How can he answer?
Answer: Rav taught about a case in which the openings are not opposite each other.
Question: [If so,] why do we need Rav's teaching in addition to the Beraisa? (What Chidush does he add?)
Answer: One might have thought that the Beraisa teaches that it is Reshus ha'Yachid mid'Oraisa, to be Mechayev one who throws to there from Reshus ha'Rabim, but one may not carry there. Rav teaches that one may carry there.
MAVO'OS OF DIFFERENT SHAPES
(Abaye): If a Mavoy is shaped like a centipede (many small Mavo'os branch off on its sides, no two openings to Reshus ha'Rabim are opposite each other), one makes Tzuras ha'Pesach for the main Mavoy. Then, each branch is permitted through a Lechi or Korah. (See Perush Chai diagram, Perek 1 number 85, in the English Charts section.)
Objection #1 (Rava): This is like Shmuel, who considers a bent Mavoy to be closed [at the bends. It needs only a Lechi or Korah at the openings.] If so, Tzuras ha'Pesach is not needed!
Objection #2 (Rava): There was a bent Mavoy in Neharda'a. They were stringent like Rav [to consider it Mefulash, even though this was Shmuel's region. This shows that we do not follow Shmuel!]
(Rava): Rather, one makes Tzuras ha'Pesach at one side of each [small] Mavoy (where it meets the main Mavoy) and a Lechi or Korah at the other side.
(Rav Kahana bar Tachlifa): If one side [wall] of a Mavoy is longer than the other (like Rashi's diagram), and the excess is less than four Amos, one puts the Korah on the diagonal (resting on the ends of the walls). It permits everything inside;
If the excess is four Amos [or more], one must put the Korah (straight) even with the short side [like the second diagram in Rashi].
(Rava): In both cases one must put the Korah even with the short side.
I hold that a Korah is for a Heker. If it is on a diagonal, there is no Heker [past the end of the short side. It looks like people carry there in Reshus ha'Rabim];
Rav Kahana holds that a Korah is for a Mechitzah. Even on a diagonal, it is a Mechitzah.
(Rav Kahana): One may put the Korah on a diagonal only if the diagonal is at most 10 Amos. If it is more than this, all agree that one must put it even with the short side.
Question: Does the Heter to carry in the Mavoy include the place underneath the Korah?
Answer #1 (Rav, R. Chiya and R. Yochanan): One may carry under the Korah.
Answer #2 (Shmuel, R. Shimon bar Rebbi and Reish Lakish): One may not carry under it.
Suggestion: Those who permit hold that a Korah is for a Heker [for people in Reshus ha'Rabim, i.e. outside the Mavoy. Someone under the Korah appears to be inside the Mavoy.] Those who forbid consider a Korah like a Mechitzah. (It is as if the inner edge extends down to the ground (Pi Tikra Yored v'Sosem). Under the Korah is outside the Mavoy.)
Rejection #1: No, all agree that a Korah is for a Heker. Those who permit hold that the Heker is for people in Reshus ha'Rabim. Those who forbid hold that the Heker is for people inside the Mavoy.
Rejection #2: No, all agree that a Korah is for a Mechitzah. Those who permit apply Pi Tikra Yored v'Sosem to the outer edge. (Under the Korah is inside the Mavoy.) Those who forbid apply it to the inner edge.
(Rav Chisda): All forbid carrying in the area even with the thickness of the Lechi.
Question (Rami bar Chama): If two pegs stick out of a Mavoy, one from each wall, and a Korah rests on top of them [and touches the walls], what is the law?
Answer #1 (Rav Chisda): The opinion that permits [carrying under a normal Korah, because Pi Tikra Yored v'Sosem applies to the outer edge] forbids [the entire Mavoy. The Korah does not permit it, for the thickness of the Korah separates the 'wall' created from the opening of the Mavoy];
The opinion that forbids [under the Korah, because Pi Tikra Yored v'Sosem applies to the inner edge] permits. (The 'wall' created seals the opening.)
Answer #2 (Rava): All forbid. The Korah must be on top of the [walls of the] Mavoy.