Eruvin 90A

לנטורי תרביצא הוא דעבידא.

that he built the upper story to protect the garden [tarbitza], not to access the roofs.

בעי רמי בר חמא: שתי אמות בגג ושתי אמות בעמוד מהו? אמר רבה: מאי קא מיבעיא ליה, כרמלית ורשות היחיד קא מיבעיא ליה?

Rami bar Ḥama raised a dilemma: According to Rav, who holds that one may carry only within 4 cubits on each roof, if he carries an object two cubits on a roof and another two cubits on a pillar 10 handbreadths high and 4 handbreadths wide adjacent to the roof, what is the halakha? Rabba said: With regard to what matter is he raising a dilemma? Is it with regard to a karmelit and a private domain that he is raising a dilemma? The roof is a karmelit and the pillar is a private domain; certainly carrying from one to the other is prohibited.

ורמי בר חמא אגב חורפיה לא עיין בה, אלא הכי קמיבעיא ליה: שתי אמות בגג ושתי אמות באכסדרה, מהו?

The Talmud explains that this was not in fact the dilemma, and Rami bar Ḥama, due to his keen mind, did not analyze the dilemma carefully and was imprecise in its formulation. Rather, this is the dilemma he is raising: If one carries an object two cubits on the roof of a house, and another two cubits on the slanted roof of a portico, a roofed structure without walls, before a house belonging to someone else, what is the halakha?

מי אמרינן: כיון דלא האי חזי לדירה ולא האי חזי לדירה ⁠— חדא רשותא היא. או דילמא: כיון דמגג לגג אסיר, מגג לאכסדרה נמי אסיר.

The Talmud elaborates on Rami bar Ḥama’s dilemma: Do we say that since neither this roof is fit for residence, nor is this portico roof fit for residence, it is regarded as one domain, and therefore carrying between them is permitted? Or perhaps since carrying from a roof to another roof is prohibited, carrying from a roof to a portico is likewise prohibited, as the latter is also a domain in and of itself.