Explanation #1 (Rashi): [Rabah bar Avuha] did not permit to be Me'arev the entire city together, even though it was a small city, and a Mishnah below says that we may be Me'arev all of an individual's city.

Objection and Explanation #2: Below (60a) we say that it was a city of Rabim! It says that Rabah bar Avuha was Me'arev all of Mechuza by neighborhoods - each was a remnant for the other;

An individual's city does not need a remnant, unless it was previously a city of Rabim! Rather, surely it was a city of Rabim.

Support: Also above (6b) connotes that it was of Rabim, regarding the Mavo'os Mefulashim of Mechuza. [Ula] said that had they not locked the doors of at night, one would have been liable for it due to Reshus ha'Rabim. This implies that there were 600,000 people in it;

In any case, if not for [date] pits in trenches, they could have been Me'arev the entire city together, and they would have left over 50 residents according to R. Yehudah, or three Chatzeros according to R. Shimon.

Explanation #1 (Rashi): Mechuza was a city without a wall. They made a Mechitzah at the end of the Mavo'os on each side to guard [date] pits;

It is not considered a Mechitzah to join the Mavo'os and make the entire city like one, because the surrounding was not done for the sake of the city, rather, to guard pits in trenches.

Inference: It was Hukaf before the city was inhabited, for if it was Hukaf afterwards, this was done also for the sake of the city, and it is a proper Mechitzah.

Question #1: The wording connotes that had they removed the [date] pits, it would have been a proper Mechitzah. According to Rashi, even if there were no pits there, it would not be permitted, since it was Hukaf and later inhabited!

Question #2: Rashi explained that Mechuza did not have a wall. This is wrong. It says above (6b) that in the Mavo'os Mefulashim of Mechuza, they locked the doors at night!

Explanation #2: It was surrounded by a wall, after it was inhabited. They could have been Me'arev all of it together, if not for the [date] pits in trenches, which were between one neighborhood and another along the length of the Mavuy. It was more than Beis Sa'atayim, and 10 [Tefachim] deep;

They could not be Me'arev from one neighborhood to another, because they could not carry from one to another, for the pits were a Karfef more than Beis Sa'atayim;

It is unlike the stack of Peros above (24b, which is considered for the sake of residence). Those were proper for people to eat.

Even though [the trenches are 10 deep, so they] have Mechitzos, they does not help at all, for they are walls for guarding.

Explanation #3 (Rashi below, 60a): [They could not be Me'arev the entire city together] due to the pits that interrupt, and they cannot go from one neighborhood to another;

[The trench] is like a ditch between two Chatzeros. We say below (78b) that they may be Me'arev separately, but not together.

Rebuttal: Here it connotes unlike this. Rather, it is because it is a wall for guarding.

Question: Perhaps our Mishnah discusses when he was explicitly Mevatel the Reshus of his house!

Answer #1: If so, why did [R. Ila'i] not find anyone else who says so?!

Answer #2: Our Mishnah connotes [to the Makshan] that it discusses even Stam.

Explanation #1: Only among [R. Eliezer's] Talmidim [R. Ila'i] did not find anyone else who says so], for in a Beraisa in Pesachim (39a, R. Ila'i) said "until I came to R. Eliezer ben Yakov, and he agreed to my words" (that Arkavlin is Kosher for Maror).

Explanation #2: [R. Ila'i means that] he did not find anyone else who heard [these teachings] from R. Eliezer.

Explanation (Rashi): This is a thick fiber that grows around date trees. It wraps around [the tree] and ascends, like vine sprigs.

Objection (Ri): In Pesachim (39a), we say "just like Matzah is a kind of Zera'im, also Maror is a kind of Zera'im";

Note: Really, Zera'im is something grown in order to eat the seeds. We say there that Maror is Yerek (something grown to eat the plant itself)! Perhaps "Zera'im" just means that it is not from a tree.

There we say that Charchavina (one of the five species that the Mishnah is Machshir for Maror) is Atzvasa d'Dikla (an ivy that grows around date trees)!

Answer: Perhaps [Arkavlin and Charchavina] are two [different] species, and both of them wrap around date trees.

Explanation #1 (Rashi): This refers to Eruvei Chatzeros and Eruvei Techumim.

Objection: All agree that Eruvei Chatzeros require bread (below, 71b)!

Explanation #2: Our entire Perek proves that we discuss Eruvei Techumim.

Question: In Pesachim (92a), it says that regarding an Onen (one of his seven close relatives died today), Metzora and Beis ha'Peras, if they need to bring Korban Pesach, Chachamim did not enforce their words in a case of Kares;

Explanation: They did not enforce their words to be Metamei him, because there is Kares for one who [intentionally] does not fulfill [Korban] Pesach.

Summation of question: Here it connotes that even for the sake of Eruv, [Chachamim] did not enforce their words (they allow a Kohen to go through a Beis ha'Peras)!

Also there [they permit going through a Beis ha'Peras] through Rav Yehudah's method of checking (30b), for it says regarding Beis ha'Peras "this is like the Mishnah says. Beis Shamai and Beis Hillel agree that we check for those who will eat Pesach, and we do not check for those who will eat Terumah";

It says "how do they check? Rav Yehudah said in the name of Shmuel, a person [bends down] and blows [on the ground] in Beis ha'Peras [before each step, to clear away any small bones that might be there] and goes through.

Implied question: In Ohalos (18:4), it explains regarding this Mishnah "how does he check? He brings earth that he could move, and puts it in a sieve with fine holes, and breaks it down to be very fine. If there is a bone k'Se'orah (the size of a barley seed), he is Tamei.

Answer: That checking is for one who already passed through. Rav Yehudah discusses one who wants to pass. He means (below, 30b) "how do they check if he wants to pass through?"

Answer: We say [in Pesachim] that Chachamim did not enforce their words in a case of Kares, i.e. because there is Kares also for one who brings Korban Pesach in Tum'ah. Therefore, only for one doing Pesach they did not enforce their words, even though there is Kares, since also if he does not do Pesach, there is Kares.

However, we do not check for those who eat Terumah, even though there is no Kares for eating Terumah b'Tum'ah, since there is Misah, they enforced their words.

Support: It says in Chagigah (25b) that they did not enforce their words for one who brings Pesach, in place of Kares, i.e. even in a place of Kares [for eating it b'Tum'ah]. They enforced their words for those who eat Terumah, in a place of Misah, i.e. even though there is no Kares, and only Misah, like I explained;

However, here, regarding Tum'as Kohen, there is no Kares, only a Lav. They did not enforce their words in place of a Mitzvah;

Even if one may be Me'arev for a matter of Reshus, it is normal to be Me'arev only for a Mitzvah, like it says below (82a).

Distinction: For a great Mitzvah, they permitted [going through a Beis ha'Peras] even without blowing, e.g. to learn Torah, marry a woman or go to judgment and contend with [Nochrim] in order to save [his property] from them, like it says in Avodah Zarah (13a) and below (40a).

Source: Since it does not bring there Rav Yehudah's teaching, this connotes that it discusses without blowing. This is why it mentioned these Mitzvos, and did not mention others.

Support: We find that for Kevod ha'Beriyos, they permitted to become Tamei mid'Rabanan, in Brachos (19b) regarding "we used to skip over coffins [in order to greet kings]."