Implied question: According to Rashi, since they think that Korah permits like a wall, what is the reason for the one who says a Tefach? There is no Mechitzah for less than four (Tefachim)!

Answer: We need not be concerned for this, since it is a wall, just we need to diminish it, like Rashi explained regarding this below.

Explanation: Since it was not disqualified, i.e. a plank four [Tefachim] remained, for a Kosher Mavuy does not lose its status of Kosher, until [the wall] is decreased and there is no remnant of four (therefore, four Tefachim suffice).

However, the beginning of a Mavuy, i.e. there is not a plank of four that remained, and he must be Machshir it, it requires four Amos.

Support: The wording connotes like this. It says "if there is there a plank of four." This connotes that [Sof Mavuy] discusses when a plank of four remained there.

Remark: Rashi's Perush (Sof Mavuy is a Mavuy that was disqualified. Since it was Kosher, a plank four Tefachim suffices. To be Machshir a Mavuy from the beginning, four Amos are needed) is unreasonable.

Implied question: When Rav Yosef said four [Tefachim], he means that Mashehu more [than four], for if the Mavuy is only four Tefachim wide, it does not need a Lechi, like Rav Ahilai below (12a). If it is not Mashehu [longer than this], its length equals its width (and it is not permitted through a Lechi or Korah)!

Answer: In any case, in that Mashehu there is no room for pillars to stand.

Explanation (Rashi): A Tefach of the opening is in the middle wall, and three Tefachim are on the wall that extends from it, and similarly on the other side.

Rebuttal: He was not precise. If so, the width of the opening is only the diagonal of [a rectangle] three Tefachim [long] by a Tefach [wide]. We clearly see that the diagonal of three by one (i.e. the excess of the diagonal over the longer side) is less than the diagonal (its excess) of a Tefach by a Tefach (throughout Shas we rely on the approximation that this is two fifths)!

Note: See the picture on the left below Tosfos. There is a triangle whose sides are 1) The diagonal of three by one, 2) The diagonal of one by one, and 3) Two. Any side of a triangle is always less than the sum of the other two sides (for the shortest path between two points is the straight line connecting them). It follows that the diagonal of three by one is less than two more than the diagonal of one by one, therefore its excess over the longer side (three) is less than the excess of the diagonal of one by one. Tosfos could have directly proven that according to Rashi, the diagonal is less than four, for this is the sum of the other two sides. However, one could entertain that it is only Mashehu less, and Rashi was imprecise only by Mashehu. Tosfos proves that the diagonal is less than three and two fifths. Rashi's imprecision is not just Mashehu.

Implied question: Why don't we bring a proof from below (10a)? Shmuel taught in the name of Levi that a Mavuy that is 20 wide, one makes a plank 10 [Tefachim] tall and four Amos long, and erects it along the length of the Mavuy!

Answer: Perhaps to divide a Mavuy into two Mavo'os, Rav Yosef agrees that four Amos are needed.

Question: Rav Yosef himself said below (10a) about Rav Huna's words (that if a Lechi looks like an extension of the Mavuy wall, if it is less than four Amos, it is considered a Lechi. If it is [at least] four Amos, it is considered a Mavoy), that (we learn from this) that the extent of a Mavoy is four Amos!

Poor answer: It is difficult to say that [there, Rav Yosef means that four Amos are needed to] remove it from the law of a Lechi (but even less than four Amos is considered like a Mavuy).

Observation: This is unlike the case below (10a) of a Lechi that continues from the wall of a Mavuy. There, it continues outside the Mavuy along the length of the Mavuy, for it is considered Shavah mibi'Fnim (it is not noticeable from inside the Mavoy);

Here, it protrudes to the width of the Mavuy and [partially] seals it, for it says below that a Mavuy seven [wide] is permitted through Omed Merubah Al ha'Parutz (the majority of the side is closed, and the minority is open).

Observation: Abaye could have brought [a support for himself, that less than four Amos is not considered like a Mavuy] also from there.

Explanation: We rely on it [to be a Lechi, to permit], even though it was not fixed there to be a Lechi, for we hold like Abaye regarding a Lechi that was set up me'Elav (without intent to be a Lechi).

Even according to R. Tam, who rules like Rava (that Lechi ha'Omed me'Elav is invalid), in any case here we discuss according to Rav Huna, and Abaye inferred below (15a) from Rav Huna (that Lechi ha'Omed me'Elav is valid).

Explanation (Rashi): Here we discuss when it was not fixed there to be a Lechi, since [Rav Huna] distinguished between four and less than four. If it was made to be a Lechi, it is Kosher in every case. Because he [made it thicker] and closes more, it is not worse than a Lechi Mashehu, like Rashi just explained!

However, the case below (10a) of a Lechi that continues [from the wall of a Mavuy], since it is along the length of the Mavuy, and it does not seal it. It is considered to be a Mavuy, even if it was fixed for the sake of a Lechi;

Support: This is why below (10a), when [Rav Yosef] infers from this teaching three matters, he did not say "we learn from it four, [including] that a Lechi ha'Omed me'Elav is considered a Lechi."

Observation: [Also] below (9b, it says) "according to R. Shimon ben Gamliel, it should be like Nir'eh miba'Chutz v'Shavah mibi'Fnim", and Rashi explained that this is how people erect a Lechi. They draw it out a little to the outside.

Inference: Even though it was fixed to be a Lechi, it is considered like a Mavuy.

Implied question: According to the opinion that Lechi Mishum (is for the sake of a) Mechitzah, it should help more if it seals [the Mavuy]!

Answer: Even so, [that opinion] requires a little Heker.

Implied question: When he erected it for the sake of a Lechi, according to Rashi it helps even if there is no Heker!

Answer: Even so, we can say that when it was erected it for the sake of a Lechi, there is publicity, and there is a Heker.

Explanation: We discuss a Mavuy wider than eight. If it were only eight, wherever he erects [the other Lechi, it permits, for] Omed Merubah!

Implied question: (Why is this a Kal v'Chomer?) Chatzer and Mavuy are the same! When they are square, a plank [four Tefachim wide] is required. If the length exceeds the width, they are permitted through a Lechi or Korah!

Answer: Even so, he properly makes a Kal v'Chomer, for when Lechi or Korah do not help, i.e. in a square [Chatzer or Mavuy], Omed Merubah helps;

The Kal v'Chomer is for the fourth wall, that Omed Merubah should help.

Observation: We cannot learn that Omed Merubah should help for all four walls, for Dayo (it suffices) to learn from a Kal v'Chomer to be like the source [from which we learn, in this case] like a Lechi.

Implied question (Rashi): Also a Mavuy eight Amos [wide], we can permit it also through this Kal v'Chomer, for this plank is more than four [Tefachim], and a plank four wide permits a Chatzer!

Answer #1 (Rashi): Since it was not fixed for the sake of Lechi, and not to permit through a plank, just like it does not get the law of a Lechi, it does not get the law of a plank.

Answer #2 (Ri): It is unreasonable to learn what is considered a plank from a Chatzer, for in a Chatzer, a plank helps like a wall. Therefore, all the more so it helps when it seals the Chatzer more;

However, a Mavuy, for which Chachamim were lenient [to permit] though a Lechi, even according to the opinion that it is due to a Mechitzah, it needs that it is called a Lechi.

Distinction: However, regarding Omed Merubah, it is a good Kal v'Chomer, for it is a full Mechitzah that helps for all four walls, but a Lechi or plank helps only for the fourth wall.

Implied question: We should say that a plank four Amos Yochi'ach (refutes the Kal v'Chomer)! It helps for a Chatzer, but not for a Mavuy. I can say the same about Omed Merubah!

Rejection #1: Since one cannot learn from it a Kal v'Chomer (that it should help for a Mavuy), one cannot say that it is Yochi'ach (to refute a Kal v'Chomer).

Rejection #2: A plank four Amos helps only for the fourth wall. You cannot learn from it to Omed Merubah, which helps for all four walls.

Question: We should learn this itself from the Kal v'Chomer from a Chatzer, which can have a breach up to 10 Amos! Why does Rav Huna say that [it can be only four Amos]?

Answer: This Kal v'Chomer does not apply to a breach of 10, due to Hi ha'Nosenes (the very reason for the Kal v'Chomer is a reason to say oppositely);

Because a Mavuy is permitted even through a Lechi Mashehu (of any thickness, the tolerance for) a breach is [only] four [Amos].

Implied question: According to the other version below (10a) that says about Pasei Bira'os (planks surrounding a well, which permit carrying inside), since they gave one leniency, they gave another leniency [we should say similarly about a Mavuy]!

Answer: There (Pasei Bira'os, Chachamim) gave excessive leniencies for Olei Regalim (people ascending to Yerushalayim for the festival), due to their hardship (getting water on Shabbos).

Question: If so, what was the question "you cannot learn from a Chatzer, for it can have a breach up to 10!"? This is not difficult at all! Hi ha'Nosenes! Because we permitted it only through Omed Merubah, we allow a breach up to 10!

Answer: We say Hi ha'Nosenes only to destroy a Kal v'Chomer. We do not say it to reject a challenge [to a Kal v'Chomer] to sustain the Kal v'Chomer.

Question: We should make a Kal v'Chomer from a Lechi or Korah! It does not help in a Chatzer, but it helps in a Mavuy. Omed Merubah [helps in a Chatzer. All the more so it helps in a Mavuy]!

Answer: We can say that a breach 10 Amos is Yochi'ach.

Implied question: We should learn [from a Kal v'Chomer] that Lechi or Korah do not help in a Mavuy [since they do not help in a Chatzer, even though it can have a breach 10 Amos], and Omed Merubah does not help in a Chatzer [since they do not help in a Mavuy, even though Lechi and Korah help there! This is according to Rav Huna, who holds that Omed Merubah does not help in a Mavuy.]

Answer: A tradition from Sinai teaches that [Omed Merubah] helps in a Mavuy]! (Maharshal - mid'Oraisa, a Chatzer and Mavuy are Reshus ha'Yachid due to three walls. What tradition is needed for them? Tosfos means that there was a tradition that when Chachamim will decree, they should permit these. Maharsha - we discuss a Mavuy Mefulash. A tradition teaches that a Lechi or Korah makes it Reshus ha'Yachid mid'Oraisa to obligate one who throws into it. This is like the opinion that both of them are due to Mechitzah.)

Implied question: We should learn that Lechi or Korah help in a Chatzer (since they help in a Mavuy, even though Omed Merubah does not help there)!

Answer #1: A tradition teaches that we need a plank four Tefachim. (Sefas Emes - perhaps he means that the Amora'im had a tradition about the initial enactment.)

Answer #2: We cannot learn from Omed Merubah (that Lechi or Korah permits even where Omed Merubah does not, and all the more so where Omed Merubah permits), for Omed Merubah permits on all four sides (and a Lechi or Korah does not);

And we cannot learn [the Kal v'Chomer in the other direction] from a Mavuy (a Lechi or Korah permits it, even where Omed Merubah does not; and all the more so a Chatzer, which even Omed Merubah permits, Lechi or Korah permits it), for its breach is only four Tefachim according to Rav Huna.

Question: He should permit because we hold below (16b) that Parutz k'Omed is permitted!

Answer: Here we hold according to Rav Huna brei d'Rav Yehoshua, who holds below (15b) that Parutz k'Omed is forbidden.

Question: Why is it a Safek mid'Rabanan? We hold that bi'Ydei Adam, Efshar Letzamtzem (one can be exact), for we hold like Rav Papa, who says that Parutz k'Omed is permitted;

If it were not Efshar Letzamtzem, we should be concerned lest Parutz Merubah!

Also in Chulin (28b), they argue about [Simanei Shechitah that were cut] halfway, whether or not it is like the majority. This implies that Efshar Letzamtzem!

Implied question: We say in Yevamos (28a) that we do not have a Stam Tana [of a Mishnah] like R. Yosi ha'Gelili, who says that Efshar Letzamtzem!

Answer #1: This refers to bi'Ydei Shamayim.

Implied question: In Gitin (78a), regarding a Safek whether [the Get] is closer to him or to her, it says "we should see which of them came first. If you will say that they came at once, Iy Efshar Letzamtzem!"