Sukkah

we say that the edge of the roof [of the exedra is regarded as though it] descends and fills up [the space],1 while Raba says it is invalid, since we do not say that the edge of the roof descends and fills up [the space]. Said Raba to Abaye, According to you who say that the edge of the roof [is regarded as though it] descends and fills in [the space, is a Sukkah valid] even if the middle wall is missing?2 He answered him, In that case I agree with you [that the Sukkah is invalid] since it would be like an alley-way that is open on two opposite sides. Must we say that Abaye and Raba differ on the same principle as that on which Rab and Samuel differed for it was stated, If an exedra was in a field,3 Rab declares that it is permitted to carry [on the Sabbath] over the whole extent of it, since we say that the edge of the roof descends and fills in the space,4 while Samuel said that it is forbidden to carry in it except within four cubits, since we do not say that the edge of the roof descends and fills in [the space]?5 — [No!] With regard to the opinion of Samuel neither of them6 disagrees;7 the missing walls? Samuel? the Sabbath where the roof was made for the exedra its edge is not regarded as descending and forming walls how much less could an edge be regarded as descending and forming walls in the case of a Sukkah where the roof was made for the exedra and not for the Sukkah.