Explanation #1 (Rashi): It is Metamei everything around it for four Amos, like a grave.

Rebuttal (R. Shimshon): Since there are tall walls, and there is no concern lest he go on top of the house and tower above it, we should not say that it is Metamei four Amos around it.

Source: This is proven in Sotah (44a) regarding the Chatzer of a grave. One who stands in it is Tahor. This is only for Chatzer ha'Kever, which has tall walls, but in general, [a grave] is Tofes (seizes the four Amos around it, and is Metamei them).

Explanation #2 (R. Shimshon): The case is, there are many ledges sticking out from the house in every direction, and each has a Pose'ach Tefach (towers over a cubic Tefach).

If he did not remove the doorposts and lintel, even if he closed it, it is not Metamei under the other ledges, since Stam, the Mes is destined to leave through an opening;

However, if he removed the doorposts and lintel, and returned and built them like a regular wall, and there is no opening at all, it is Metamei all around, for every ledge, there is a Safek if he will take the Mes out of the house from under that ledge.

Defense of Explanation #1: Also a house is not Mesaimei Mechitzta (we do not say that tall walls avert the chance of Tum'ah). Even though there is no concern lest he go on top of the house, in any case there is concern lest he touch the walls;

A grave is Metamei through touching, even from the side, like is proven in the Sifri in the Parshah of Parah Adumah;

Citation (Sifri): "B'Kever" is a sealed grave. Or, perhaps it is open? A Kal v'Chomer refutes this. An Ohel, which is Mekabel Tum'ah, is not Metamei all the sides around it when it is open;

Citation (cont.): A grave, which is not Mekabel Tum'ah, all the more so it is not Metamei all the sides around it when it is open!

Inference: When it is sealed, it is Metamei even one who touches it from the side.

Explanation: This is when they became established to use it with permission. However, if they come to establish using it without permission, he can protest against them and hold a stick and sit there [and strike people who go there], like is proven in Bava Kama (28a).

Explanation (Rivam): In the place of R. Yehudah, the land was important and good, and it was worth toiling for nine half-Kabim;

However, in the place of the first Tana, the land was not so good that it would be worth toiling for less than nine Kabim.

Even though (nine or nine half-Kabim) is not large enough to plow for an entire day (it is inefficient to hire workers or rent animals for less than a day's work), it was worth toiling for.

Now, we ask what is the law in Bavel? The land was not so good, and it is not proper [to work a field] the size taught in our Mishnah.

Explanation: This is the area one plows in one day. This properly requires a day when seeding;

When he comes to seed it, he plows, and in his return, he again pulls the plow on the land and seeds it. This is "b'Hadurei" (in his return).

Implied question: We asked that this is not two days of plowing [before the time of seeding]!

Answer: He plows [before the time of seeding] for a day and a half, and plows again until the day ends.

Explanation #1 (R. Chananel): Land that they irrigate with a bucket, everyone must receive a land that takes [at least] one day to irrigate.

Objection (Ri): If so, it should have asked "what is the amount in Bavel", like it asked in the other cases!

Explanation #2: It seems that Rashi's explanation is correct. (We divide a pit only if everyone receives a share for which it is one day's labor to irrigate land from it.)

Explanation: [R. Yosi] did not say so to praise [Sumchus' opinion], rather, to say that there is no reason for it.

Support #1: We find like this in Bechoros (45a) regarding an extra finger without a nail. (If it was cut off,) it is Metamei through touching or moving, but not b'Ohel;

Citation (45a - R. Yochanan): They made their words like words of prophecy! No matter what you will say, this is difficult! If it is a limb, it should be Metamei b'Ohel. If it is not a limb, it should not be Metamei at all!

Support #2: It is proper to explain like this in Eruvin (60b).

Question: In Sanhedrin (75a), it says that after Churban Beis ha'Mikdash, the pleasure of Bi'ah was removed, and given to transgressors;

We should challenge [Rav Avdimi, who inferred that those who received, did not have it before] also [there], before the Churban, did [transgressors] not have pleasure of Bi'ah?! We learn from the verse "Mayim Genuvim Yimtaku", similar to how we ask here!

Answer: We can answer there like we answer here, that pleasure of Bi'ah was removed, but it was not removed from transgressors. The Gemara was not concerned to ask this in every place.

Implied question: In Bava Kama (80b), Rav Acha himself said that [once evil befalls a person,] they never do good to him!

Answer: Initially, he said that they are not quick to do good to him. He hoped that they would return him to his greatness. When he saw that they did not return him, he later said that they never do good to him (one to whom evil started to come).

Explanation: This is like we learn below (124b) from "Pi Shenayim." It equates the [extra] share of a Bechor to the regular share.

Version #1: Some texts say after this "the sisters said..." If so, "Bei Nashyah" is his father-in-law. His father-in-law had no sons, only daughters.

Version #2: Some texts say "the brothers said..." If so, "Bei Nashyah" is his father. (See Tosfos Shabbos 23b DH d'Vei Nashya.)

Question (Ri): According to Rabah, why do we need a verse for a Bechor, that we give to him on one border? (In any case we do so, for Kofin Al Midas Sedom!)

Answer #1 (Ri): This is because the Torah gave to him rights only like two brothers. If two brothers wanted to join, we do not force the third to give to them a share together.

Answer #2: The Torah calls [the extra portion of] a Bechor "a gift", like it says below (124a) "Lases Lo Pi Shenayim", and we do not force a giver [to give in a particular way].

Also according to Abaye (who learns from a verse that a Yavam can demand to receive his shares together, he can hold that Kofin Al Midas Sedom.) Had the Torah not called [a Yavam] "Bechor", one might have thought that "Yakum Al Shem Achiv" as if he and his brother are alive. (They cannot demand to receive adjacent shares.)

Explanation (Ritzva): Rabah says that Kofin Al Midas Sedom. This is not based on Torah law, for according to letter of the law the other party can protest, for there is adamancy about the directions, like it says in several places;

Also, Kofin Al Midas Sedom is when this one benefits and this one does not lose, i.e. he already lived in his friend's Chatzer, that he does not pay wages;

However, obviously he can protest that he not enter to live in his house, even in a Chatzer that is not standing to be rented, and a man who does not normally pay rent, in which case this one benefits and this one does not lose!

Rather, [Rabah] said here due to an enactment of Chachamim that we force.

Answer #3 (to Question (a)): Now it is not difficult at all why we need a verse for a Bechor.

Explanation #1 (Rashi): Regarding a Sedeh ha'Ba'al (rain suffices for it. One need not irrigate it), they can say that sometimes it is blessed more than other fields;

Regarding two fields on two rivers, we cannot say Mailinan (they cannot say that it is worth more), since he needs to irrigate it, and one is not blessed more than the other.

Rebuttal #1: Also those [fields] that must be irrigated, sometimes one is blessed more, for one is stricken through blasting, and one is not stricken.

Explanation #2 (R. Tam): Mailinan like property of Bar Meryon, i.e. we will not give to you rights that we have in this field, if not for a high price, like Bnei Meryon, who were rich, and they sold their lands only for a high price.

"Two fields on two rivers" does not refer to the episode of that man (who bought property near the land of his father or father-in-law). Rather, it is an independent matter;

I.e. there are two fields, each of which has a river, and one [brother] wants to divide each into two, that he will take half of each;

Rabah said that Kofin Al Midas Sedom, and each takes a whole field, so each will have a portion on one border.

Support: So we can explain two fields on one river. The river separates between the two fields. If they will divide each field into two, his portion will not be on one border.

Support: Now, with these, we cannot say Mailinan like property of Bei Bar Meryon. If one wanted to divide to 20, will we say that they divide due to Mailinan?!

Rebuttal #2 (of Explanation #1): The expression "Mailinan" cannot be resolved according to Rashi.