1. There is a dispute in the Mishnah about the status of roofs.
2. The Gemara explains the reasoning of the Chachamim.
3. The Gemara discusses how one may carry on a roof of a house when there are no walls surrounding the airspace of the roof.
4. The Gemara explains the Chachamim's statement, "Every yard is its own domain."
5. Rav Yosef and Abaye similarly disagree about the Chachamim's opinions about how far one may carry on the roof.
A BIT MORE
1. Rebbi Meir: They are considered one domain if one is not higher or lower than ten Tefachim from the next roof. Chachamim: Each roof is its own domain. Rebbi Shimon: They are all one domain with regard to vessels that were in them at the onset of Shabbos.
2. The Chachamim say that just as every house is considered a separate domain and one may not carry from one to the other without an Eruv, the roofs in the neighborhood are considered separate domains.
3. Rav: One may carry only for four Amos, as the walls of the house are not considered noticeable enough on the roof to permit carrying on the basis of the principle of Gud Asik. Shmuel: One may carry on the entire roof since the walls of the house render the roof a private domain due to the principle of Gud Asik.
4. Shmuel: This means simply that one may carry on the entire roof. Rav: This means that one may not carry two Amos on one roof and continue carrying another two Amos on another roof.
5. Rav Yosef agrees with Rav. Abaye pointed out to Rav Yosef that before Rav Yosef became sick and forgot his learning, he agreed with Shmuel.