Question: When they were not Me'arev with each other, why is the one that did not make the Ukah forbidden?

Answer (Rav Ashi): This is a decree, lest people take Kelim [with water] into the Chatzer to spill it.

(Mishnah - R. Meir): All roofs of the city are considered one Reshus (one may transfer between them if they are open to each other), as long as a roof is not 10 Tefachim higher or lower than the adjacent roof;

Chachamim say, every roof is a separate Reshus. (One may not transfer between them without an Eruv);

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

(Gemara - Abaye bar Avin and Chanina bar Avin) Question: We understand Chachamim. They hold that just like the residences are separate below (belong to different people), they are separate above. (Therefore, an Eruv is needed.) However, what is R. Meir's reasoning?

If he holds that just like residences are separate below, they are separate above, why are the roofs one Reshus?

If he does not consider the roofs to be separate, for everything above 10 is one Reshus, why does it matter if a roof is 10 Tefachim higher or lower than the adjacent roof?

Answer (Abaye - R. Yitzchak bar Avdimi citing R. Meir): Whenever there are two [similar] adjacent Reshuyos (both are Reshus ha'Yachid), such as a pillar 10 tall and four wide standing in Reshus ha'Yachid, one may not adjust a load on it;

This is a decree, lest one do so on a mound (10 tall and four wide, it is Reshus ha'Yachid) in Reshus ha'Rabim.

Here also, R. Meir decrees due to a mound in Reshus ha'Rabim!

Assumption (Chanina and Abaye bar Avin): He decrees even regarding a mortar or barrel [that is 10 tall and four wide].

Rejection (Abaye citing Rabah): R. Meir decrees only about a pillar or base of a millstone, for people fix places for these.

Question: A wall between two Chatzeros is fixed, yet Rav Yehudah taught that R. Meir holds that roofs are a Reshus by themselves, and likewise Chatzeros, and likewise Karfifos;

Suggestion: One may go over the wall between Chatzeros to transfer between them! (We do not decree due to a mound in Reshus ha'Rabim.)

Answer (Rav Huna bar Yehudah): No, one may transfer between Chatzeros via openings between them.

(Mishnah - Chachamim): Every roof is a separate Reshus.

(Rav): One may not carry more than four Amos on any roof [if it is open to another roof, since it is totally open to a Reshus to which one may not transfer];

(Shmuel): One may carry on the entire roof.

If the walls [of the houses] can be seen from the roofs (there is a space between them), all agree [that one may carry on the entire roof. We say Gud Asik Mechitzta (it is as if the walls extend upward and divide between the roofs);

They argue in a case when the walls cannot be seen from the roofs (there is no space between them);

Rav forbids carrying more than four Amos on a roof. We do not say Gud Asik;

Shmuel permits the entire roof. We say Gud Asik.

Question (Mishnah - Chachamim): Every roof is a separate Reshus (one may carry in it itself).

This is like Shmuel, but it is unlike Rav!

Answer (Bei Rav citing Rav): No. It is called 'a separate Reshus' to forbid carrying two Amos in one roof and two Amos in another (i.e. to transfer between them. It does not permit an entire roof.)

Question: R. Elazar said that in Bavel, Bei Rav said in the name of Rav that one may not carry more than four Amos on a roof, and Talmidim of Shmuel taught a Beraisa saying that they may carry only on the roof;

Suggestion: The Beraisa permits carrying on the entire roof!

Answer: The Beraisa does not permit this more [explicitly] than the Mishnah does. Just like we answered that the Mishnah merely forbids transferring between roofs, we explain the Beraisa similarly!

Rav Yosef: I never heard this teaching [of Shmuel].

Abaye: You taught it to us regarding the following teaching!

If a wide roof borders a narrow roof (see Perush Chai diagram, Perek 9 number 14, in the English Charts section) one may carry anywhere in the wide roof. One may not carry more than four Amos on the narrow roof. (This is even like Rav. We say Gud Asik all around [because the walls of the houses are Nikarim], except for the border between the roofs, so the wide roof is fully surrounded on three sides. It is permitted because even the fourth side has Gifufun (walls on both sides of the opening). The narrow roof is forbidden, since it is totally open on one side [to the wide roof].)

(Rav Yosef citing Shmuel): This is only if there are Diyurin on both roofs (residents who go from roof to roof), for then Rabim trample over the [imaginary] Mechitzah. (In such a case, we do not say Gud Asik);

If there are not Diyurin on top of both of them, both roofs are permitted. (We say Gud Asik.)

Rav Yosef: No. Rather, I taught the following:

This is only if there are [real] Mechitzos around both roofs (except for the border between them). The wide roof is permitted due to Gifufun, but the narrow roof is forbidden, since it is totally open [on one side];

If there is no Mechitzah around either roof, both of them are forbidden.

Abaye: You said that it depends on Diyurin!

Rav Yosef: I did not mention Diyurin. Perhaps I said that it depends on Dirah! (Rav Yosef forgot his learning):

This is only if there is a [fixed] Mechitzah proper for Dirah around both roofs. The wide roof is permitted due to the remnants [on its fourth side, where it borders the narrow roof], but the narrow roof is forbidden, since it is totally open [on one side];

If there is a Mechitzah proper for Dirah around the wide roof but not around the narrow roof, both roofs are permitted to [the owners of] the wide roof.

Question: What is the reason?

Answer: Since [the owners of] the narrow roof did not make a Mechitzah for their roof, this shows that they withdraw from it [and concede it to the wide roof], similar to Rav Nachman's teaching;

(Rav Nachman): If [the owners of] one roof fixed a ladder to alight to it (but the adjoining roofs did not), all the roofs are permitted to that roof.

(Abaye): If one built an Aliyah on top of his roof (surrounded it with walls), and made a Dakah (small opening four Tefachim wide) to an adjacent roof, all the adjoining roofs are permitted to him (he shows that he plans to use them. Since the others did not protest, this shows that they concede their roofs to him - Rashi. Tosfos - the case is, all the [owners of the] roofs were Me'arev together except for one. If that one makes a Dakah, i.e. Mechitzah in front of his roof, he does not forbid the others.)

(Rava): Sometimes the Dakah forbids [even according to R. Meir], e.g. if he surrounded his roof with walls, and made a Dakah only to his garden. He shows that the Aliyah is for guarding his garden [and not to access the roofs].