On daf 2a, the gemara said that according to Rebbi Zeira the Chachomim hold that a sukka higher than 20 amos is Pasul because the Sechach does not provide shade to the lower part of the Sukah when it is so high. Abaye asked that if this is the reason then we should invalidate a sukka between two mountains. The gemara answers that "there the Sukah would still be valid even without the sun-blocking mountains, whereas our Sukah would not be valid (since its Sechach does not generate any shade at all) without the walls." Then on daf 2b, Rav Huna said in the name of Rav that the Chachamim agree if the sukka's area is more than 4 by 4 and the gemara explained that he's going with the reason of R' Zeira.
The gemara on 3a asks a question on Rav Huna from Hilni Hamalka because she was sitting in a sukka that was more than 20 amos high and yet the Rabbanon didn't say anything to her and R' Yehuda uses this as a proof. The gemara answers that was a case where the sukka had many small rooms so the room may have been smaller than 4 by 4.
My question is why according to R' Zeira and R' Huna is that a pasul sukka? Why don't we say that you could just remove the inner walls and then the schach would give shade so this should be no different than the sukka between two mountains?
David Greenstone, Baltimore, US
As you point out from the Gemara on 2a, the pertinent factor is that the S'chach of the Sucah must be capable of providing shade in the Sukah. The idea of "removing the mountains" is just the way the Gemara illustrates the fact that the Sukah itself is capable of providing shade. In the case of the Kitoni'os, each room is considered an individual Sukah, since it is separated from the rest of the Sukah by a Mechitzah. The shade provided by the S'chach that is outside the walls of the Kitoni'os is not shade of the Sukah the person in the Kitoni'os is sitting in. The S'chach of each of the Kitoni'os is incapable of providing shade to the Kitoni'os, and as such is invalid. We cannot imagine that the walls were not here and say that the Sukah is Kosher since the shade comes from outside the Sukah.