Gemara

90a - Question (Rami bar Chama): May one transfer between his roof and a pillar?

Objection: Does he ask about transferring from a Karmelis to Reshus ha'Yachid?! [Surely one may not!]

Correction: Rather, he meant to ask whether one may transfer between his roof and the roof of an Achsadra.

93a - Question (R. Hoshaya): Do dwellers who come on Shabbos (i.e. the wall that separated from them fell) forbid?

Answer (Rav Chisda - Mishnah): If a wide Chatzer was breached to a narrow Chatzer, the wide Chatzer is permitted, and the narrow Chatzer is forbidden, for it is like an opening of the wide one.

Rejection (Rabah): Perhaps the wall fell before Shabbos.

Abaye (to Rabah): Why do you say perhaps? You must say that it fell before Shabbos [for you accepted the following answer of Rav Huna]!

Question (Rabah): If one was Me'arev through an opening or window and it became sealed [on Shabbos], what is the law?

Answer (Rav Huna): Once Shabbos was permitted, the Heter stands.

(Rav): If the wall between two Chatzeros fell, one may not carry [in either Chatzer] more than four Amos;

(Shmuel): People of each Chatzer may carry up to where the wall was.

Rav's law was inferred from an episode in which he and Shmuel were in a Chatzer. The wall between it and the adjoining Chatzer fell.

Shmuel: Spread a garment where the wall used to be.

Rav turned his face away [to shows that he forbids. He did not explicitly protest, for it was Shmuel's region.]

Shmuel spread a garment merely for privacy. Even without it, he permits carrying up to where the wall was.

(Mishnah - R. Eliezer): If [the wall of] a Chatzer was breached to Reshus ha'Rabim, one who throws from it to Reshus ha'Yachid or vice-versa is liable;

Chachamim exempt one who throws from it to Reshus ha'Rabim or vice-versa, for it is a Karmelis.

(Mishnah - R. Yehudah): If [on Shabbos] a Chatzer or house was breached on two sides, or if the Lechi or Korah was removed from a Mavoy, it is permitted for that Shabbos and forbidden in the future;

R. Yosi says, if it is permitted for that Shabbos it is permitted in the future. If it is forbidden for the future it is forbidden for that Shabbos.

95a (Rav Sheshes and R. Yochanan): R. Yosi forbids.

(R. Chiya bar Yosef): The Halachah follows R. Yosi.

(Shmuel): The Halachah follows R. Yehudah.

(Rav Anan): Shmuel explained to me that the Halachah follows R. Yehudah if it is breached to Karmelis, but not if it is breached to Reshus ha'Rabim.

17a (Rav Huna): If there were three people and one died [on Shabbos], or if there were two people and another came [on Shabbos], their status (individuals or a caravan) depends on the number of people at the start of Shabbos;

(R. Yitzchak): It depends on the number of people currently there.

R. Yosi could hold like Rav Huna. R. Yosi forbids only when there are not Mechitzos. Here the Mechitzos are intact!

Rishonim

Rif and Rosh (30b and 9:3): The Halachah follows Shmuel, for we hold that residents who come on Shabbos do not forbid. Once part [of Shabbos] was permitted, all of it is permitted.

Hagahos Ashri: Surely, the next Shabbos is forbidden. See Or Zaru'a.

Rambam (Hilchos Eruvin 3:25): If two Chatzeros made an Eruv through an opening between them or a window, and on Shabbos the opening or window was sealed, each is permitted by itself. Once part was permitted, all of it is permitted. Similarly, if each of two Chatzeros made an Eruv by itself, and on Shabbos the wall between them fell, each may carry up to where the wall was. Once part was permitted, all of it is permitted. Even though new residents came, residents who come on Shabbos do not forbid.

Rebuttal (Ra'avad): In the first case, there is no need to say that each is permitted by itself! Rather, they may even transfer from one to the other, like before the opening or window was sealed.

Tosfos (93b DH Lo): Abaye says that Rabah holds like Shmuel. In Shabbos (22a), he said that Rabah was always stringent like Rav with only three exceptions [and this is not one of them]! Perhaps he does not count Eruvin and Avelus, in which the Halachah follows the lenient opinion. Alternatively, sometimes Shmuel's leniency is a stringency, e.g. it was forbidden for part of Shabbos, therefore it is forbidden for all of Shabbos. This is not considered a stringency of Rav. Just like he does not say that once it was permitted, it is permitted, he does not say that once it was forbidden, it is forbidden.

Tosfos (95a DH u'Shmuel): We establish the argument of Rav and Shmuel to be when it was breached to Karmelis. It seems that the Halachah follows Rav in Isurim. Even when it was breached to Karmelis, the Halachah follows R. Yosi, who is stringent. When the Mechitzos are intact, even R. Yosi agrees, like it says on 17a.

Tosfos (Shabbos 9a DH Af): If the doorway of a house opens to Karmelis, when the door to the house is closed, one may transfer from the doorway to the Karmelis.

Rashi (Eruvin 24a DH l'Kula): If a Chatzer was breached to a Karfef more than Sa'atayim, the latter is a Karmelis, so even R. Shimon forbids transferring from the Chatzer to the Karfef.

Avodas ha'Kodesh (Beis Nesivos Sha'ar 3, Siman 1, 33,34): Some say that a platform at the opening of a Mavoy that is three tall and less than four wide is Mekom Petur. I say that any place surrounded by three walls is Reshus ha'Yachid. One may not transfer from it to the Reshus it opens to, whether it is Reshus ha'Rabim or Karmelis.

Poskim

Shulchan Aruch (OC 374:2): If there was a wall between two Chatzeros, and each Chatzer made an Eruv by itself, and on Shabbos the wall was breached, each may carry in its Chatzer the entire Shabbos.

Kaf ha'Chayim (11) and Bi'ur Halachah (DH v'Nifratz): It was totally breached, or more than 10 Amos. Less than this is an opening [which does not forbid].

Mishnah Berurah (7): Even though now each Chatzer is breached to a Reshus in which it is forbidden, since it was permitted Bein ha'Shemashos, it is permitted for all of Shabbos.

Shulchan Aruch (ibid.): We permit even Kelim of the house.

Beis Yosef (DH v'Chen): Shmuel permits even Kelim of the house. If they were in the Chatzer at the start of Shabbos, one may take them even from Chatzer to Chatzer! The Rif, Rambam and Rosh rule like Shmuel.

Mishnah Berurah (8): Kelim of the Chatzer are permitted even to the other Chatzer, because all Chatzeros are one Reshus (372:1).

Shulchan Aruch (ibid.): However, if the wall of the Chatzer was breached on Shabbos to Reshus ha'Rabim or Karmelis, it is forbidden.

Gra (DH l'Reshus): This is like Rav. See Tosfos 95a.

Beis Yosef (DH u'Mah she'Chasav Oh): In many places in Eruvin, we forbid carrying in a Chatzer totally breached to Karmelis. The Tur says that this is even if it was breached on Shabbos, like the Mishnah. We rule like R. Yosi, who forbids that very Shabbos.

Question: The Poskim rule like Shmuel, who permits like before the wall fell. Surely this is because once part was permitted, all is permitted!

Answer (Beis Yosef): There is different, for it was breached only to another Chatzer, which is also Reshus ha'Yachid. The only difference between them is the owners. When it is breached to a truly different Reshus, i.e. Reshus ha'Rabim or Karmelis, we do not say "once part was permitted, all is permitted." The Chatzer itself becomes a Karmelis. A breach to Reshus ha'Rabim or Reshus ha'Yachid is more stringent than a breach to Karmelis. In the former cases, one may not transfer from the Chatzer to the Reshus it was breached to, even within four Amos. If it was breached to Karmelis, this is permitted.

Magen Avraham (3): When it is breached to a Karmelis, the Beis Yosef permits transferring from the Chatzer to the Karmelis within four Amos. Perhaps even though it was breached, it is still called a Chatzer, and one may not transfer from it to a Karmelis. See Daf 6a and 24a.

R. Akiva Eiger: Tosfos (Shabbos 9a) permits. Also Rashi (90a DH u'Beis) says that we ask about from a roof to the roof of another's Achsadra. Surely, we permit from his roof to the roof of his Achsadra. However, there both roofs are Reshus ha'Yachid mid'Oraisa, so this is not a proof. Tosfos (90a DH Ela) brings that R. Chananel (our text - R. Tam) explains that he initially asked about from a roof that is Reshus ha'Yachid to a pillar nine tall, which is a Karmelis [and the Gemara rejected this, for surely it is forbidden]!

Hagahas R. Akiva Eiger's son: See Tosfos 25b (DH Ela. At the end, he permits transferring from a Karfef more than Sa'atayim to a proper Karmelis.)

Bi'ur Halachah (DH l'Karmelis): Tosefes Shabbos and R. Akiva Eiger brought a proof to permit from Tosfos (Shabbos 9a). Nehar Shalom brought that Avodas ha'Kodesh explicitly forbids. Tosefes Shabbos proved that Rashi (24a) forbids. Therefore, one may not be lenient.

Kaf ha'Chayim (15) Nehar Shalom says that the Rambam permits. Chemdas Moshe gives another reason to forbid.