תלמוד על עירובין 9:1

They asked before Rebbi Abba: Concerning what you are saying about a window between two courtyards, is it the same for a window between two houses? He told them, yes. Is it the same for a window between two roofs? He told them, yes. May one make an eruv across skylights²⁵Between the living quarters and the flat roof.? Rebbi Abba Mari said, it is a disagreement between Rav and Samuel, as we have stated there: “All roofs of a city are one domain.²⁶Mishnah 9:1.” Samuel said, up to two bet se’ah; Rav said, one may move inside them even a kor, even two kor²⁷The Mishnah does not spell out what kind of domain is formed by the roofs. For Samuel, roofs are places which are not fenced in for dwellings; they follow the rule of corrals where carrying is only allowed if the surface area is at most 5’000 square cubits. If the total area of the roofs is larger, an eruv would be ineffective; the roof cannot be part of the eruv domain of the house. But for Rav one is permitted to carry on connected roofs without limitations (even if the total area be larger than 2 bet kor, 60 bet se’ah); the eruv may be extended to the roof. The Babli has a very different tradition, 89a–90b..

MISHNAH: Rebbi Jehudah says, up to two bet se’ah⁴In his opinion the maximal size of domain for which double planks are authorized are the standard 5’000 square cubits.. They said to him, two bet se’ah were said only for a garden patch⁵An irrigated vegetable garden. and a corral⁶For cattle.. But if there was a sheep-pen, or a sheep corral, or a backyard, or a front yard, even five bet kor⁷A kor is 30 seˋah; a bet kor 75’000 square cubits., even ten bet kor are permitted and it is permitted to put them arbitrarily far away on condition to add planks³The distances between two planks cannot be greater than those described in Mishnah 1, 5 cubits for R. Meïr and 14 for R. Jehudah..

Rav and Rebbi Joḥanan say, it is forbidden both on this Sabbath and the coming Sabbath⁵⁹In Mishnah 4, practice is decided following R. Yose; since it is forbidden in the future it must be forbidden now..