(Mishnah): If five groups spent Shabbos in a hall (each has an opening to the Chatzer), Beis Shamai say [each group is considered a separate Reshus, so they need an Eruv to transfer among each other.] Each group must be Me'arev (give towards the Eruv in the Chatzer);

Beis Hillel say that [they are considered one Reshus, so they may transfer among themselves without an Eruv.] One Eruv [in the Chatzer suffices] for all of them.

[Beis Hillel] agree that if they are in rooms or attics, each must be Me'arev.

(Gemara): The hall in front of them is like a Chatzer is to houses. If there were Mechitzos between the groups, it is as if they are houses (even Beis Hillel obligate an Eruv).

Question: What is the case?

If the Mechitzos reach the ceiling beams, all agree that every group needs its own Eruv;

If the Mechitzos do not reach the ceiling beams, all agree that they make one Eruv for all of them!

Answer: The case is, the Mechitzos are 10 [Tefachim] tall [but do not reach the ceiling].

They agree that if they are partners in a dough or Tavshil (cooked food), they make one Eruv for all of them.

Question (Rav Shein): If so, even if some of them dwell in rooms or Aliyos (one Eruv should suffice for all of them)!

(R. Ba citing Rav Yehudah): If there are two houses, one inside the other, if the inner [house] was Me'arev, the outer need not be Me'arev. If the outer was Me'arev, the inner must be Me'arev.

(R. Pinchas): [Matanos of Dam Pesach] in Mitzrayim was opposite. If he put on [the doorposts and lintel] of the inner [house], he must put on [those of] the outer. If he put on [those of] the outer, he need not put on the inner. (This is based on MASA D'YERUSHALAYIM, with a change.)

(R. Yakov bar Acha citing R. Avahu citing R. Yehoshua ben Levi): Even if the inner was not Me'arev (e.g. its residents are not here), the outer need not be Me'arev (it does not forbid the Chatzer). What is the reason? It is considered like a Beis Sha'ar.

His (R. Yehoshua ben Levi's) words show that [the law of] a Beis Sha'ar applies to an individual (a lone house is inside). Rav's words show that a Beis Sha'ar does not apply to an individual;

(R. Ba bar Yehudah citing Rav): (A Mishnah teaches that an Eruv placed in a Beis Sha'ar is invalid, and one who lives there does not forbid even if he is not Me'arev.) This refers to a Beis Sha'ar of Rabim, but a Beis Sha'ar of an individual, an Eruv placed there is valid, and one who lives there forbids. (We explained this like MEICHAL HA'MAYIM and HA'GAON RAV C. KANIEVSKY, SHLITA.)

(R. Ba bar Yehudah citing Rav): If two people [live in a house in a Chatzer], one of them has Reshus (it is his house) and one of them does not have Reshus - if the one who has Reshus was Me'arev, the one who does not have Reshus is permitted;

If the one who has no Reshus was Me'arev, the one who has Reshus is not permitted.