Eruvin 89B

רשות לעצמו. בשלמא לשמואל ניחא, אלא לרב קשיא.

is a domain in and of itself. This indicates that each roof constitutes a discrete domain, and one may carry throughout this entire domain. Granted according to the opinion of Shmuel, this works out well, but according to the opinion of Rav, it is difficult.

אמרי בי רב משמיה דרב: שלא יטלטל שתי אמות בגג זה, ושתי אמות בגג זה.

The Talmud answers that the rabbis of the school of Rav said in the name of Rav: The ruling in the Mishnah is not a leniency permitting one to carry throughout the entire roof; rather, it is a stringency, ruling that one may not move an object two cubits on this roof and two cubits on that roof. The tanna rules that even the allowance to carry within 4 cubits is restricted to a single roof.

והא אמר רבי אלעזר: כי הוינן בבבל הוה אמרינן: בי רב משמיה דרב אמרו: אין מטלטלין בו אלא בארבע אמות, והני דבי שמואל תנו: אין להן אלא גגן.

The Talmud raises a difficulty. But didn’t R' Elazar say: When we were in Babylonia we would say that the rabbis of the school of Rav said in the name of Rav: One may move an object on each roof only within 4 cubits, and those rabbis of the school of Shmuel taught a baraita in accordance with their opinion: They have only their own roof.

מאי ״אין להן אלא גגן״, לאו דשרו לטלטולי בכוליה? ומי אלימא ממתניתין, דאוקימנא שלא יטלטל שתי אמות בגג זה ושתי אמות בגג זה?! הכי נמי, שתי אמות בגג זה ושתי אמות בגג זה.

The Talmud seeks to clarify this baraita. What is the meaning of the statement: They have only their own roof? Is it not that they are permitted to move an object throughout each entire roof? This baraita poses a difficulty to Rav. The Talmud rejects this contention: And is this baraita any stronger a proof than our Mishnah, which we established as a stringency, that one may not move an object two cubits on this roof and two cubits on that roof? So too, this baraita is teaching that one may not carry two cubits on this roof and two cubits on that roof.