Explanation (R. Tam): [Also he] did like Yakov Avinu (who established coinage, markets or bathhouses for Shechem), and fixed a matter.

Explanation: This is like it says in Nidah (61a). A Beraisa says that R. Yosi ben Shaul says that a case occurred with a rock which was established to have Tum'ah [under it];

He told them to bring sheets. They brought to him. He soaked them in water and spread them [on the ground]. The place of the Tum'ah was wet, and the place of Taharah was dry.

Explanation #1 (R. Tam, Rashi, R. Chananel): We are stringent about Eruvei Techumim, because they have a support from a verse.

Support: The Yerushalmi says so, and Eruvin (46b) connotes like this regarding "the Halachah follows the lenient opinion about Eruvin;

Citation (46b - Rav Papa): [R. Yehoshua ben Levi needed to rule like R. Yochanan ben Nuri,] for one might have thought that the Halachah follows the lenient opinion only regarding Eruvei Chatzeros, but not regarding Eruvei Techumim.

Explanation #2: Initially, R. Tam explained that Eruvei Chatzeros are more stringent, for they are only with bread, like it connotes in Eruvin (71b) and Chulin (81a), but one may use anything for Eruvei Techumim, except for water and salt.

Rebuttal: R. Meir holds that Eruvei Techumim are mid'Oraisa, in Eruvin (35a), and even so, he holds in Eruvin (71b) that Eruvei Chatzeros are [only] with bread, and one may use [almost] anything for Eruvei Techumim;

We do not find that R. Meir argues with the Stam Mishnah in Eruvin (26b), that one may use anything [for Eruvei Techumim];

The reason we are lenient about Techumim and do not require bread is because we are Me'arev only for a Mitzvah.

Explanation: This is not precise. The same applies if it was not eaten.

Explanation #1 (Rashi): Rava discusses Eruvei Techumim.

Support: The words "go make an Eruv" connote like this. (One must go far to make it.)

Implied question: When it is Safek dark, we may not make Eruvei Techumim!

Answer: That is l'Chatchilah. B'Di'eved it is Kosher, like R. Yosi, who said (Eruvin 35a) that a Safek Eruv is Kosher.

Question (Rashba): There, R. Yosi holds that if a rockpile fell on it, or it burned, and Terumah became Tamei (and we are unsure if this was during the day or at night), the Safek Eruv is Kosher, only due to Chazakah (that it was still intact), like a Beraisa teaches there explicitly (36a)!

Citation (36a): How did R. Yosi say that a Safek Eruv is Kosher?... However, a Safek like here, that he left it Bein ha'Shemashos, or it was eaten Bein ha'Shemashos, he is not Machshir.

Explanation #2 (R. Tam and R. Chananel): Here we discuss Eruvei Chatzeros.

Support: This is proven in Eruvin (76a).

Rejection of Support (b): We find that "go" refers also to matters not outside the city, e.g. "go hire workers for us" (Bava Metzi'a 83a).

Explanation (Rashba): There is a Safek only when it is like an eye's blink, but not during a long time, like the Safek of the first Tana.

Suggestion: R. Yosi has no Safek about Bein ha'Shemashos at all. He means "I recognize it and I am expert about it like an eye's blink, to know when [the coming day] enters and [the previous day] ends. I know when it is day, and when it is night."

Rejection: The Tosefta in Zavim (1:13) teaches "and so said R. Yosi. If one saw one [emission of Zov] Bein ha'Shemashos and one Vadai, he is a Safek for Tum'ah and Korban;

Explanation: He saw on Motza'ei Shabbos Bein ha'Shemashos, and on Monday. He is a Safek for Tum'ah - perhaps all of Bein ha'Shemashos is day, and there was a day without Zov (Sunday) in between, and he is Tahor. (In this discussion, "Tahor" means Tamei like a Ba'al Keri, but he does not need seven clean days);

Or, perhaps all of Bein ha'Shemashos is night, and there were two consecutive days [of Zov], so he is Tamei (he needs seven clean days);

Or, perhaps part of Bein ha'Shemashos is day, and part is night, and there were three consecutive days [of Zov], and he is obligated a Korban.

Inference: Also R. Yosi is unsure about the eye's blink (whether it is day or night or partly each).

Explanation #1 (Rashi): Perhaps all of the first Bein ha'Shemashos is day, and all of the second is night.

Rebuttal #1: If all of the first is day, also all of the second is day!

Rebuttal #2: It says below in our Sugya (35b) that if one does Melachah during two Bein ha'Shemashos (Erev Shabbos and Motza'ei Shabbos), no matter what you will say, he is obligated a Chatas. (Really, he did Melachos each Bein ha'Shemashos. If it was one prolonged Melachah, e.g. carrying in Reshus ha'Rabim, perhaps he did only half on Shabbos.)

According to Rashi, we can say that perhaps all of Bein ha'Shemashos of Erev Shabbos is day, and all of it on Motza'ei Shabbos is night, so he is not Chayav Chatas, rather, Asham!

Explanation #2 (Rashbam): He is a Safek for Tum'ah and Korban - he saw Bein ha'Shemashos on Motza'ei Shabbos, and Bein ha'Shemashos of Monday evening;

Perhaps both Bein ha'Shemashos are totally day, or both are totally night. A day interrupts in between, and there is no Tum'ah;

Or, perhaps part is day, and part is night. The days [of Zov] were consecutive, and he is Tamei seven days and he is obligated a Korban.

Objection #1: "Two days Bein ha'Shemashos" connotes consecutive days.

Objection #2: According to this, we do not find seven days of Tum'ah without a Korban. The words of the Gemara connote that the Safek of Tum'ah and the Safek of Korban are separate (do not depend on each other).

Objection #3 (Ri): If we discuss when he saw all of Bein ha'Shemashos, like the case of one who did Melachah on two Bein ha'Shemashos, like the Rashbam explained, if so, when he saw one he is Chayav Korban, for Bein ha'Shemashos is at least [the time to walk] half a Mil;

This is 1000 Amos, for the Shi'ur of a Mil is 2000 Amos, like Rashi explained in Yoma (60a);

It says in Sanhedrin (63a) that if one saw a sighting [of Zov] as long as three sightings, which is [the time to walk] from Magdiyon to Shilo, which is like the time for two immersions and two dryings, he is a total Zav (he must bring a Korban);

In the Tosefta (Zavin 1:10-11), it connotes that this Shi'ur is [the time to walk] 100 Amos!

Explanation #3 (R. Tam): We discuss that he did not see all of Bein ha'Shemashos, rather, a small time during this Bein ha'Shemashos and another time during another Bein ha'Shemashos;

For any amount of time Bein ha'Shemashos, there is a Safek that it is totally during the day, or totally at night, or half day and half night;

Now there is a Safek of Tum'ah - perhaps the first [sighting] was totally day, and the second was totally night, and a day interrupts in between [so he is Tahor];

Or, perhaps both were during the day, or both were at night, and there are two consecutive days (he is Tamei, but exempt from a Korban):

There is a Safek of Korban. Perhaps the first was [half] during the day and [half] at night, and the second was at night, or the first was during the day, and the second was half during the day and half at night, and there are three consecutive days.

Explanation #3 (cont.): The case of one who did Melachah on two Bein ha'Shemashos, this means that he did Melachah all of Bein ha'Shemashos, or he did both times at the beginning [or both times at the end] of Bein ha'Shemashos.