Rabah bar Rav Huna used to go to Pumbadisa on Shabbos. (From his house he would declare his Shevisah to be in a specific place in that direction.)

Abaye: Do you think that because R. Yehudah argues with R. Meir, the Halachah follows R. Yehudah, and Rav Chisda said that they argue about declaring Shevisah elsewhere?! Rav Nachman argues with Rav Chisda, and a Beraisa supports him!

Rabah bar Rav Huna: I retract. I will not do so again.

(Rami bar Chama): If one was Me'arev through walking, he has four Amos [in addition to 2000 Amos in every direction];

Question (Rami bar Chama): If one placed an Eruv, does he have four Amos [in addition to 2000]?

Answer (Rava - Mishnah): An Eruv with bread is a leniency for Ashirim, so they need not walk.

If one who places an Eruv does not have four Amos, it is a stringency, and not a leniency!

Rejection: Even so, he prefers that he need not walk. It is a leniency.

(Mishnah - R. Yehudah): If Reuven was walking towards another city for which one needs an Eruv to go there, and Shimon met him and persuaded him to go back, Reuven may go there. The rest of his city is forbidden.

R. Meir says, anyone who could have been Me'arev, but was not, is in Chamar Gamal.

(Gemara) Question: Why is he different than the rest of his city?

Answer (Rav Huna): The case is, Reuven has one house here, and another house 4000 Amos away in the other city. He intended to go to his other house, and not to be Me'arev. Therefore he is like an Oni. He can declare his Shevisah to be at the end of the Techum. The rest of his city are Ashirim.

Support (Beraisa - R. Yehudah): If Reuven has one house here and another 4000 Amos away in another city, once he starts to go towards his other house, he acquires an Eruv (i.e. Shevisah, even without saying anything);

R. Yosi b'Rebbi Yehudah taught a bigger Chidush. Even if Shimon met him and told him 'stay here, for it is too hot or cold [to go]', Reuven may go the next day.

(Rabah): All agree that Amirah is required (he must declare his Shevisah - Rashi's preferred explanation. See note 16 in Appendix for other explanations);

They argue about whether or not he must have started walking. (R. Yosi permits even if Shimon heard Reuven's intent and dissuaded him before Reuven started walking.)

(Rav Yosef): All agree that he needs to have started walking. They argue about Amirah. (R. Yehudah requires it, and R. Yosi does not).

Question: Like whom does Ula hold?

(Ula): If Reuven started to walk and Shimon returned (dissuaded) him, he is returned and Muchzak (in the Shevisah he desired to get).

Question: If he is returned (from acquiring Shevisah outside the city), he is not Muchzak (in that Shevisah)! If he is Muchzak, he is not returned!

Answer: It means that even though he returned, he is Muchzak.

Answer: It is like Rav Yosef's explanation of R. Yosi b'Rebbi Yehudah. (He did not declare his Shevisah.)

Rav Yehudah bar Ishtesa brought a basket of fruit to R. Noson bar Oshayah (4000 Amos away). When he was leaving [on Erev Shabbos], R. Noson waited until he took a step down from the Aliyah, and told him 'stay tonight, and return tomorrow.'

Suggestion: This is like Rav Yosef's explanation of R. Yosi b'Rebbi Yehudah! (Rav Yehudah did not declare his Shevisah.)

Rejection: No, [he declared his Shevisah.] It is like Rabah's [or Rav Yosef's] explanation of R. Yehudah [who requires that he started walking].

(Mishnah - R. Meir): Anyone who could have been Me'arev, but was not, is in Chamar Gamal.

Question: We already learned this in another Mishnah (35b)!

(Mishnah - R. Meir and R. Yehudah): If we are in Safek [whether an Eruv became disqualified before or on Shabbos], he is in Chamar Gamal.

Answer (Rav Sheshes): One might have thought that R. Meir holds that Chamar Gamal applies only to a Safek Eruv. Our Mishnah refutes this. Here he definitely was not Me'arev, and he is in Chamar Gamal [for he did not want the Techum of his city, and he did not acquire another Techum].

(Mishnah): If someone went even one Amah outside the Techum, he may not re-enter;

R. Eliezer says, if he went two Amos outside he may re-enter, but not if he went three Amos outside.

Version #1 (Gemara - R. Chanina): If someone has one foot in the Techum and one foot outside, he may not re-enter. "Im Tashiv mi'Shabas Raglecha (if you will hold back your feet due to Shabbos)" is written without a Yud, suggesting one Regel (foot).

Question (Beraisa): If one foot is in the Techum and one is outside, he may re-enter.

Answer: That is like Others:

(Beraisa - Others): A person is considered to be where the majority of his body is.

Version #2 (R. Chanina): If one foot is in the Techum and one is outside, he may re-enter - "Im Tashiv mi'Shabas Raglecha" - we pronounce it "Raglecha" (plural, he is forbidden only if both feet are outside).

Question (Beraisa): He may not re-enter.

Answer: R. Chanina holds like Others:

(Beraisa - Others): A person is considered to be where the majority of his body is.

(Mishnah - R. Eliezer): If he went two Amos outside he may re-enter, but not if he went three Amos outside.

Contradiction (Beraisa #1 - R. Eliezer): If he went one Amah outside he may re-enter, but not if he went two Amos outside.

Resolution: The Beraisa means that if he totally left one Amah and is standing in the second, he may re-enter, but not if he totally left two Amos and is standing in the third.

Contradiction (Beraisa #2 - R. Eliezer): If he went even one Amah outside he may not re-enter.

Answer: That refers to one who [declared his Shevisah to be in his place and] measures his Techum [by counting 2000 steps]:

(Mishnah): We learned that one who measures his Techum gets 2000 Amos. Even if they end at a cave, he may not enter it. (Since the 2000 Amos was in addition to his four Amos, we do not give him any more.)

(Mishnah): If one was traveling and he was outside the Techum when it became dark, even if he was only one Amah outside he may not enter;

R. Shimon says, even if he was 15 Amos outside he may enter, for those who measure do not put the Techum marker at the full 2000 Amos, due to people who err [and walk past it. Alternatively, those who measure the Techum err, i.e. they grasp the rope in their hands, consuming a Tefach and a half finger on each side of the rope. (Perhaps the extra half finger sticks out below the hand, or vertically above, until it gets horizontal - PF.) Each 50 Amos measured lacks two Tefachim and a finger. The total deficit in 2000 Amos is 80 Tefachim and 10 Tefachim (40 fingers), i.e. 15 Amos.]

(Beraisa): This is due to those who err about the measure.

(Mishnah) Question: How are we Me'abar a city (append outskirts before measuring its Techum)?

Answer: [If a line of houses is a wall of the city,] a house that juts out extends the city;

A tower that juts out from the wall extends the city;

The following [extend it] if they have a place of Dirah - Gedudiyos (broken remnants of ruined houses) 10 Tefachim tall, a bridge, and a Nefesh (Aruch - a monument over a grave; Rashi - a watchman's quarters over a grave).