1) A RESIDENT OF THE CHATZER WHO DIED ON SHABBOS
QUESTION: Rabah says that one who forgot to join the Eruv in a Chatzer before Shabbos may be Mevatel his Reshus on Shabbos, but he must be Mevatel his Reshus to every resident in the Chatzer and not just to one of the residents. Abaye challenges this ruling from a Beraisa which states that "one who did not join the Eruv may be Mevatel his Reshus to one who did join the Eruv." Obviously, the Beraisa is referring to a case where there was at least one other person in the Chatzer besides the two individuals mentioned, because it mentions "one who did join the Eruv." If there are only two people in the Chatzer and one did not join the Eruv, with whom did the second person make the Eruv? It must be that there was at least one other person in the Chatzer, and the Beraisa says that the one who forgot needs to be Mevatel Reshus to only one person.
Rabah answers that the Beraisa refers to a case in which, at the onset of Shabbos, there were two others in the Chatzer who had made an Eruv together (besides the person who forgot to join the Eruv), but on Shabbos one of them died. When the one who forgot to join the Eruv is Mevatel his Reshus to the remaining resident, he is being Mevatel to all of the [current] members of the Eruv.
If there was another resident of the Chatzer who died on Shabbos, how can Bitul Reshus help to permit one to carry in the Chatzer? The heirs of the deceased person inherit his property in the Chatzer, and since they did not join the Eruv, their share in the Chatzer forbids the two remaining residents from carrying in it on Shabbos!
(a) RASHI (DH d'Havah) answers that the Beraisa refers to a temporary encampment in the wilderness which a group of travelers set up in order to rest over Shabbos. Since each traveler merely pitched his tent there and no one owns the property, there is no property there for heirs to inherit. When one of the travelers dies, his share in the make-shift Chatzer passes completely to the remaining residents.
(b) TOSFOS (DH Hacha b'Mai) answers that the Beraisa follows the opinion of Rebbi Shimon (47a) who maintains that if a resident of the Chatzer is away for Shabbos, his absence does not prohibit the others (who made an Eruv) from carrying in the Chatzer. In this case, when the heir inherits his father's house in the Chatzer, he is no different from an absentee owner. Since he is not present, he does not prohibit the residents of the Chatzer from carrying.
(Rashi, who does not give this answer, seems to assume that the Beraisa follows the opinion of Rebbi Meir, who says that even when a resident of the Chatzer is away for Shabbos, he still prohibits the other residents from carrying. Rashi is consistent with his opinion elsewhere in this regard (62b, DH Amar Mar, see Insights there), where he explains other Gemaros according to the opinion of Rebbi Meir.)
(c) Alternatively, Tosfos answers that even if the Beraisa follows the opinion of Rebbi Meir, who says that one who is away from his home in the Chatzer on Shabbos still prohibits the other residents from carrying in the Chatzer, the Beraisa may be discussing a case where the heir was one of the two remaining residents of the Chatzer (who had made an Eruv with his father before Shabbos).