Gemara

(Mishnah - R. Meir): All roofs of the city are considered one Reshus, as long as a roof is not 10 Tefachim higher or lower than the adjacent roof;

Chachamim say, every roof is a separate Reshus.

R. Shimon says, roofs, Chatzeros and Karfifos are all considered one Reshus for Kelim that were Shoves (began Shabbos) in them, but not for Kelim that were Shoves in the house.

91a (Rav): The Halachah follows R. Shimon, if they were not Me'arev;

If they were Me'arev, we decree, lest one transfer Kelim that were Shoves in a house to another Chatzer.

(Shmuel and R. Yochanan): [It is permitted] whether or not they were Me'arev.

91b - Support (for Rav - Beraisa): If five Chatzeros are open to each other and to a Mavoy, and all forgot to be Me'arev, one may not take Kelim from the Chatzer to the Mavoy or vice-versa;

One may move Kelim that were Shoves in the Chatzer in the Chatzer, but not in the Mavoy.

R. Shimon permits, for he holds that when Reshuyos of Rabim (many people) forgot to be Me'arev, the roof, Chatzer, Achsadra, Mirpeses, Karfef and Mavoy are all one Reshus.

Inference: This is only when they were not Me'arev!

Rejection #1: No. The Chatzeros were not Me'arev together, i.e. Shituf Mavo'os, but the houses in each Chatzer were Me'arev.

Rejection #2: R. Shimon addresses Chachamim;

I permit whether or not they were Me'arev. You should agree with me at least when they were not Me'arev that they are one Reshus!

92a - Question (Ravina): Did R. Yochanan really rule like R. Shimon? R. Yochanan said that the Halachah follows a Stam Mishnah!

(Mishnah): If a wall between two Chatzeros is 10 Tefachim tall and four Tefachim thick, the Chatzeros can be Me'arev individually, but not together;

People from either Chatzer may alight on the wall and eat Peros that are there, but they may not take them down.

Answer (Rav Ashi): They may not take them down to the house [but they may take them down to the Chatzer].

Rishonim

Rambam (Hilchos Eruvin 1:5): If a Reshus ha'Yachid is divided among residents, and each has his own Reshus, and part belongs to all of them, e.g. a Chatzer in front of houses, we enacted to view the common area like Reshus ha'Rabim, and the private areas like Reshus ha'Yachid.

Rambam (3:18): All roofs of the city, even though some are high and some are low, with all the Chatzeros and Karfifos not Hukaf l'Dirah that are each at most Beis Sa'atayim, and the thickness of the walls between Chatzeros, and Mavo'os with a Lechi or Korah, all are considered one Reshus. One may move in all of them, without an Eruv, Kelim that were Shoves in them. For Kelim that were Shoves in the house, one needs an Eruv.

Tosfos (89a DH Kol): Even though the Halachah follows R. Meir's decrees, even against a majority, the Ri says that here it does not, for the Gemara rules like R. Shimon.

Tosfos (91b DH v'Kelim): R. Shimon permits Kelim that were Shoves in the Chatzer to another Chatzer. Do not say that he permits only within the Chatzer. This is permitted even for Kelim that were Shoves in the house!

Poskim

Shulchan Aruch (OC 372:1): R. Shimon says, roofs, Chatzeros and Karfifos are all considered one Reshus for Kelim that were Shoves in them.

Beis Yosef (DH Chatzer): It seems that the Halachah follows R. Yochanan against Rav, especially since Shmuel holds like R. Yochanan. The Poskim rule like this, unlike Ba'al ha'Itur, who rules like Rav. Rashi explains that R. Shimon holds that since roofs, Chatzeros and Karfifos are not a special, constant usage, they are one Reshus. One may transfer from one to another, even from a Chatzer of Rabim to a Chatzer of Rabim without an Eruv. R. Shimon holds that Eruvei Chatzeros are needed only for Kelim of the house.

Mishnah Berurah (3): Eruvei Chatzer is needed also for carrying from the Chatzer to the house.

Magen Avraham (1): One may not transfer Kelim that were Shoves in the house from the Chatzer to a Karfef not Hukaf l'Dirah, even if one person owns both. The Rambam connotes that an Eruv helps for Kelim that were Shoves in the house, and all the more so if one person owns [the Reshuyos]. This requires investigation. The Gemara connotes unlike this. Perhaps the Rambam does not refer to a Karfef [regarding what an Eruv permits].

Mishnah Berurah (1): 'Roof' connotes that there no ceiling over it. An Aliyah (second story) with a roof on it is like the house. Their roofs were flat and proper for use. We discuss roofs that do not stick out from the walls of the house.

Bi'ur Halachah (DH Gagin): Also Mavo'os are one Reshus with them. The Mechaber adopted the text of the Mishnah, and relies on what he wrote below.

Shulchan Aruch (ibid.): One may transfer them from one to the other, even if there are many different owners who were not Me'arev together. One may transfer from a Chatzer to another Chatzer...

Mishnah Berurah (5): This means that the Chatzeros were not Me'arev with each other. It is a bigger Chidush to permit when the people in a Chatzer were Me'arev together, like we say below!

Beis Yosef (DH u'Mah she'Chasav Rabeinu): The Tur discusses a Chatzer open to another Chatzer. Really, it is permitted even if it is not open to another Chatzer, through a roof or Karfef in between. The Tur discusses a typical case. When they are open to each other, one transfers from one to the other.

Shulchan Aruch (ibid.): ... [Or one may transfer] to the roof, or to the top of a wall between them, or from a roof to an adjacent roof, even if it is much taller than it...

Mishnah Berurah (8): We do not say that the height difference divides them into separate Reshuyos.

Shulchan Aruch (ibid.): ... [Or one may transfer] from a roof to a Karfef less than Sa'atayim, or was Hukaf l'Dirah, even if it is more than Sa'atayim...

Mishnah Berurah (10): More than Beis Sa'atayim that was not Hukaf l'Dirah is Karmelis. One may not take from Reshus ha'Yachid to it.

Shulchan Aruch (ibid.): ... [Or one may transfer] to a Mavoy fixed through a Lechi or Korah, even if they were not Me'arev, and even if the Bnei Chatzer were Me'arev by themselves, and Kelim from the house are common in the Chatzer.

Mishnah Berurah (11): Also a Mavoy is not a constant usage. Therefore, it is the same Reshus with them. Shituf Mavo'os is needed only for Kelim that were Shoves in the house, to permit taking them to the Mavoy.

Mishnah Berurah (12): This means that the Chatzeros did not make Shituf together.

Kaf ha'Chayim (10): Since there is a Lechi or Korah, it is like a Chatzer without an Eruv. It is not like a Karmelis.

Mishnah Berurah (13): If the Bnei Chatzer were not Me'arev, Klei ha'Bayis are not common in the Chatzer at all, for one may not take them to the Chatzer. Then surely one may take Klei Chatzer to another Chatzer, for there is no need to decree about Klei ha'Bayis.

Shulchan Aruch (ibid.): One may transfer them from this Chatzer to another Chatzer. We are not concerned lest one transfer Kelim that were Shoves in the house to another Chatzer, roof, or Karfef.

Mishnah Berurah (14): The same applies to a roof or Karfef.

Mishnah Berurah (15): We are not concerned, for this would be a decree for a decree.

Mishnah Berurah (16): This shows that Kelim that were Shoves in the house, even if they came to the Chatzer b'Heter, through an Eruv, one may not take them to another Chatzer that it was not Me'arev with. The same applies if he wore them and removed them in the Chatzer.

Bi'ur Halachah (DH Shema): If Kelim that were Shoves in the house were brought to the Chatzer, some Poskim allow moving them only within four Amos. The Rashba says so, and the Rambam connotes like this. Rashi and Tosfos (91b) permit in the entire Chatzer. They hold that Chachamim forbade only transferring from one Reshus to another. Maharam Shif used this to answer R. Akiva Eiger's questions against Rashi. Even ha'Ozer permits only within four Amos even what was brought into the house. Beis Meir refuted this. Even the stringent opinions consider only a joint Reshus like Reshus ha'Rabim. R. Akiva Eiger agreed to this.

Bi'ur Halachah (DH l'Chatzer): Beis Meir says that what one was wearing at the start of Shabbos is Batel to his body. It is not like Kelim that were Shoves in the house.