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1)

(a) Even though, it takes *four Amos* of *Pasul S'chach* to invalidate the Sukah at the side - it only needs *three Tefachim* of space to invalidate it.

(b) On account of this Halachah, Rashi rejects the explanation of Dofen Akumah that we consider the wall as if it was bent and extended underneath the S'chach Pasul up to the S'chach Kasher - because, if we said *that*, then the Sukah should be Kasher even if there was up to four Amos of *space* at the side, no less than if it was S'chach Pasul.

(c) The Tana gives three examples of Dofen Akumah. Having stated ...

1. ... the case of the broken ceiling of a house, he nevertheless found it necessary to add that of the covered porch or passageway which surrounds a courtyard - whose walls were not made for the courtyard (like the walls of the house were made for the area that has now become a Sukah).
2. ... the previous two cases, he still found it necessary to add the case of the Sukah with Pasul S'chach around the side - because we might otherwise have thought that we only say 'Dofen Akumah' by materials that are at least fit for S'chach and are only Pasul because of 'Ta'aseh ve'Lo min he'Asuy'. Now we see that it applies in all cases (even if the material of which the wall was made is *not fit* to be used as S'chach at all).

(a) According to the Rabbanan de'Bei Rav, four Tefachim of Pasul S'chach will invalidate the Sukah *in the middle* of the Sukah*. *Four Amos* distance from the side constitutes the middle of the Sukah.

(b) Rabah queried them from our Mishnah, which permits Pasul S'chach op to four Amos. They replied in the name of Rav and Shmuel - that the Mishnah is referring exclusively to the side of the Sukah, where S'chach Pasul is Kasher because of 'Dofen Akumah' (but not in the middle, where the Shiur of Pasul S'chach is four Tefachim - which is a Makom Chashuv and constitutes a Chatzitzah). Note: Rabah does not hold of the principle of Dofen Akumah.

(c) Rabah attempt to disprove the Rabbanan de'Bei Rav from the case of a Sukah with less than *four* Tefachim of Pasul S'chach next to less than *three* of space, which is Kasher. If filling in that space with *Pasul S'chach* (which is more lenient than space - since the Shiur of the former is *four* Tefachim, whereas that of the later is *three*) he argues, will invalidate the Sukah, then why should the *space* (which is stricter than S'chach Pasul) not likewise invalidate it?

(d) They retorted that, in that case, Rabah should ask *himself* the self question (seeing as according to him too, the Shiur of air is even more stringent vis-a-vis S'chach Pasul - than it is according to them)!

3)

(a) According to *his* opinion, Rabah answers, four Amos is the fixed Shiur of Pasul S'chach that disqualifies a Sukah - irrespective of whether it is at the side or in the middle. Consequently, since its Shiur is not equivalent to that of space, they cannot combine to disqualify the Sukah (which explains why two and half Tefachim of space cannot complete the deficiency of two and a half Tefachim in four Amos of S'chach Pasul, whereas the same amount of S'chach Pasul can). According to the Rabbanan however, in whose opinion the four Tefachim of S'chach Pasul in the middle of the Sukah is not a Shiur, but a Sevara (that is based on the importance of four Tefachim as a Makom Chashuv), the reason that four Tefachim of Pasul S'chach invalidates the Sukah is because there is a significant area of four Tefachim without Kasher S'chach. That being the case, what is the difference whether that area is filled with Pasul S'chach or with space? Hence Rabah's original Kashya: If Pasul S'chach invalidates the Sukah, Kal v'Chomer space?

(b) Rabah vindicates himself on the grounds that according to him, it is a matter of Shiurim, and the Shiur of Pasul S'chach and that of space cannot combine, because they are different. But surely by a small Sukah, asks Abaye, the Shiurim are the same, since three Tefachim of either space or of Pasul S'chach, will render the Sukah Pasul (in which case, they ought to combine even by a large Sukah)?

(c) That is not true, answers Rabah! The reason that three Tefachim of either will invalidate the Sukah by a small Sukah, is not because of the Shiur of Pasul S'chach or space, but because there is lacking a Shiur Sukah.

(a) The Mishnah in Keilim rules that the Shiur Tum'ah of cloth is three by three Tefachim, of sackcloth, four by four, of leather, five by five, and of a mat made of platted reeds, six by six. The Tana is referring to Tum'as Mishkav or Medras - if one designated it for a Zav to lie on.

(b) Each of these will combine with the next in line (if sewn together) to become subject to the more lenient Shiur of Tum'ah - i.e. cloth with sackcloth (to a Shiur of four Tefachim), sack-cloth with leather (to a Shiur of five), and leather and platted reeds (to a Shiur of six Tefachim).

(c) *They* combine to become Tamei - because sometimes they all have the same Shiur; whereas in Rabah's case, Pasul S'chach and space never have the same Shiur.

(d) All of the above materials have the same Shiur(of one Tefach) when they are sewn as a patch into the saddle-cloth of a donkey (not necessarily sewn together).

(a) In the second Lashon, Rabah's statement is quoted in the name of Rav. Shmuel disagrees with him.

(b) Shmuel interprets the Mishnah, which *validates* a plank of four Tefachim - by establishing it at the side of the Sukah.

(c) Rebbi Meir in the Beraisa maintains that two planks combine. According to the first Lashon, they combine to make up four *Amos*, to invalidate the Sukah even in the middle of the Sukah; but according to the second Lashon, where Rav holds that in the middle of the Sukah, four *Tefachim* already invalidate the Sukah, how does the Beraisa speak? If each plank is *four* Tefachim wide, then why should it be necessary to combine two planks? Whereas if they are *less* than four Tefachim, Rav (who establishes the Machlokes between Rebbi Meir and Rebbi Yehudah in the Mishnah on 14a. by planks of four Tefachim) anything *less than four* Tefachim like canes, which are Kasher S'chach, however many combine to form the S'chach? This is not a Kashya on Shmuel, who establishes the Machlokes by planks of between three and four Tefachim, which is how he will also establish the Beraisa (and Shmuel does not consider planks to be mere canes - unless they are *less than three* Tefachim wide.

(d) Rav answers that the Beraisa speaks by planks of *four* Tefachim, that are placed at the side of the Sukah which will invalidate it if they total four Amos.

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