Implied Question: This is unlike the case of a money purse mentioned in Eruvin (79a). (Why?)

Answer: There is an opinion that people do nullify money purses as well (unlike pillows). (See the explanation of the Pnei Yehoshua on Tosfos regarding this opinion which is that of Rav Huna the son of Rebbi Yehoshua.)

Text: This is the text in all of the Sefarim here.

Text (cont.): In Eruvin (78b), the Gemara quotes this regarding the Mishnah that states that if there is a ditch between two yards that is filled with straw the yards must make separate Eruvin. However, if the ditch was filled with earth or rocks, they may only make an Eruv together, not separately. This is a Mishnah in Meseches Ohalos (15:7). It does not say in the Mishnah there, "straw" rather, "earth or rocks."

Observation: Since the Mishnah in Ohalos (15:7) is quoted in our Gemara and regarding the Mishnah in Eruvin, a mistake was made to say that the text in the Mishnah (ibid.) should read "straw" and not "earth."

Text (cont.): We do not have the text in the Mishnah, "and he nullified it, it is nullified" rather the text should read, "the impurity goes out and up and out and down." They mean essentially the same thing, as they are dependent on each other. However, the way of the Gemara is to shorten the Mishnayos it quotes from Taharos.

Implied Question: One cannot say that what is quoted here is a Beraisa (not the Mishnah in Ohalos ibid.). (Why not?)

Answer: This is because the Gemara would not quote a Beraisa if it could quote a Mishnah.

Text: This is the correct text of the Mishnah: "A house that was filled with earth or rocks and they were nullified there, and a pile of grain or rocks, even if it was like the pile of Achan, even if there is impurity on the side of the vessels the impurity goes out and up and out and down." This is because the earth and rocks etc. are nullified in the house.

Implied Question: Our Gemara says that if straw was placed there and he is not planning on taking it away, and earth was placed there with no specific intent, this is the argument between Rebbi Yosi and the Rabbanan in the Mishnah. The Gemara says this despite the fact that the Rabbanan in the Mishnah in Ohalos are not referring to straw. (How, then, can the Gemara come to this conclusion?)

Answer: The Gemara knew this because it was a Kal v'Chomer. If regarding earth and rocks the Rabbanan require nullification, certainly they require it regarding straw!

Proof: Similarly, in Eruvin (79a) the Gemara says, "Who is the Tana of Ohalos? It is Rebbi Yosi." The Gemara there continues to ask, "If it is Rebbi Yosi, we understand that he holds the opposite opinion!" The Gemara is asking regarding both straw and rocks based on the Kal v'Chomer above, even though straw was not stated explicitly in the Mishnah in Ohalos.

Explanation: When the Gemara here understands that it is obvious that if one nullifies straw it lessens the height, this is even according to the Rabbanan. This is apparent from the Mishnah in Ohalos (ibid.) that says that even a pile of grain can be nullified. Certainly this is true, then, regarding straw!

Implied Question: When the Gemara says that earth that is placed without intent is the topic of the argument between Rebbi Yosi and the Rabbanan, it could have said that the Rabbanan also argue regarding earth that he is not planning on moving, as the Rabbanan understand that such earth is not nullified unless it is explicitly nullified. They hold that not planning on moving it is not considered nullifying it, as is apparent here. (Why didn't it say the Rabbanan argue in this case as well?)

Answer: Rather, the Gemara said this case of earth that is placed without intent because of Rebbi Yosi, as he holds it is nullified even without intent.

Answer (cont.): It did not bother to say that straw and earth that is not going to be moved and earth without intent is an argument.

Question: When the shade is more than the sun, why is it valid? If you would take away the part of the branches that are higher than twenty, the rest of the branches would fall down!

Proof: This is as we find in Eruvin (3a) regarding some of the Sechach being within twenty cubits and some higher than twenty cubits that we say the Sukah is invalid. The Gemara says that if we were to take away the Sechach that is higher than twenty, there would be more sun than shade!

Proof (cont.): The explanation of the Gemara there must be that the part of the Sechach within twenty could not exist on its own, as since it is weak the wind will come and scatter it or make it fall down.

Proof (cont.): One cannot explain that even if it would stay up there would be more sun than shade, as the other Amoraim would not rule that such a Sukah is valid as it does not provide more shade than sun without including Sechach that is higher than twenty cubits. This would mean the invalid Sechach is combining with valid Sechach to cause the Sukah to be valid!

Answer: It is possible to answer that here we have more reason to say it is valid as there are a lot of branches and they could easily stay there if they would have something to lean on.

Opinion #1: This Gemara is a question on Rashi's explanation in Gitin (15b). Rashi there says regarding a case where there is a five Tefach ditch and a five Tefach wall is added onto it (above ground level) that this does not add up to a (halachic) wall of ten Tefachim. If this ditch is five Tefachim deep and he puts a wall of five Tefachim around it, it does not cause the space inside of it to be considered a private domain on Shabbos.

Question #1: However, in our Gemara regarding Sukah it is clear that this is valid! (There should be no difference between Shabbos and Sukah in this regard.)

Question #2: Similarly, the Gemara in Shabbos (7b) discusses a house that does not have ten Tefachim walls, and says that if one carved a space of four by four Tefachim in the floor the entire domain is a private domain.

Observation: However, one could answer that the Gemara in Shabbos (7b) is referring to a case where one dug four Tefachim deep by ten Tefachim tall.

Question #3: Rabeinu Tam also asks from the Gemara in Eruvin (99b) and Shabbos (99a) that says that a pit and its surrounding above ground walls combine to form a ten Tefach wall.

Question #4: Additionally, the Gemara in Eruvin (93b) says that if there are two yards one on top of the other, and there is a ditch of five Tefachim and a wall of five Tefachim (built on the floor of the top yard), Rav Chisda admits that the second yard must make a separate Eruv. This is because it has a ten Tefach wall between it and the top yard. (The top yard only has a five Tefach separation, namely the five Tefach wall, between it and the bottom yard. This shows that these two types of walls can combine, unlike Rashi.)

Opinion #2: Rather, the case of a ditch of five Tefachim and a wall of five Tefachim is only regarding the Eruv of two yards that are made one on top of the other. It is really only regarding the Eruv of the top yard (that this is not considered a wall), as is apparent from the Gemara in Eruvin (93b).

Opinion #2 (cont.): Alternatively, it is possible that if a pile of earth in the public domain that is five Tefachim high has a five Tefach wall built on top of it, it is not considered a private domain regarding Shabbos.

Question: Why isn't this considered a private domain because a person could put something there and use the area?

Proof: This is as we find in Eruvin (78a) regarding a pole that is ten Tefachim tall, four Tefachim wide, and is in the public domain that if a person puts a small peg on the width of the pole he has lessened it (and it is no longer a private domain, as he cannot use a four Tefach square surface anymore). If he fills the whole square surface with pegs it is considered a private domain, since he could now use it by putting something down on it.

Proof (cont.): The Gemara deduces from Rebbi Yochanan's statement that a pit and its wall combine to form a ten Tefach wall. In other words, just as it combines to be considered ten Tefachim deep, it also combines to be considered four Tefachim wide.

Proof (cont.): Rebbi Yochanan deduces this from the Mishnah in Shabbos (99a) and Eruvin (99b) where it says that "the wall on top of the pit that is ten Tefachim tall and four Tefachim wide." Just as certain laws apply regarding the length of ten Tefachim, so too these laws apply regarding the width of four Tefachim.

Question (cont.): Why is this considered a private domain? He cannot use its width, as the air interrupts. Rather, what could be the reason? It must be because he can put something on top of it and use it that way. Why, then, shouldn't this pile in the public domain (g1 above) be considered a private domain?

Answer: The case here is regarding a pile that is ten or twenty cubits wide like a yard. It cannot be considered a private domain because one can put something on top of it and use it, as this is only said regarding something that is narrow like a pole that is four Tefachim wide.

Question: In Shabbos (7b), regarding a house that does not have ten Tefachim inside of it and one dug into the floor of the house in order to make the inside ten Tefachim deep, why doesn't the Gemara differentiate in this fashion as does our Gemara? The Gemara should say that if there is from the edge of the ditch to the wall three Tefachim etc.?

Answer: It is possible to answer that the law of a private domain on Shabbos is different, as it is merely supposed to stop the public from walking (into this domain, and therefore this requirement is not applicable). This is unlike Sukah, where the requirement is walls that are next to the Sechach. [See Tosfos in Shabbos 7b, DH "v'Im."]

Observation: The Gemara concludes that we require noticeable walls.

Implied Question: This is unlike the case of putting Sechach on a porch that does not have beams, as discussed later (18b). (Why not?)

Answer: This is because the mouth (i.e. lip) of the roof (in 18b) is considered to be a noticeable wall.

Explanation: These are considered more recognizable as walls than a pillar, as they are recognized as being a wall (i.e. extension of the walls) of the house (as explained by the Tosfos ha'Rosh).

Implied Question: Regarding Pasi Biraos, the Gemara in Eruvin says that each side of the Passim must be one cubit (not just a Tefach). (Why in Hilchos Sukah is a Tefach sufficient?)

Answer: They were stringent regarding the laws of Shabbos.

Observation: This is also the source of the law that requires (halachic) walls to be ten Tefachim tall to be considered a wall concerning the laws of Shabbos.