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1. People who leave the Techum in order to save other Jews from attackers may carry their weapons back with them.
2. Originally, after a battle, people used to store their weapons in a house outside the Techum.
3. The Gemara explains when one is allowed to desecrate Shabbos in order to preemptively attack Nochrim.
4. The Gemara originally thought that David ha'Melech asked whether it was permitted to go to war on Shabbos in a border city (see #3).
5. The Mishnah discusses a case in which a person did not know he was within the Techum of a city when Shabbos arrived.
A BIT MORE
1. Not only are these people allowed to re-enter the Techum, they are also allowed to carry their weapons back if there is still danger from the attackers.
2. However, it happened once that the enemies realized this and returned to attack the people after they had already stored their weapons in the house, causing many deaths. Therefore, it was decreed that people should carry their weapons back to their own houses even when they were victorious, as there was still a possibility that they might be attacked again.
3. If Nochrim have gathered in order to attack Jews, the Jews are not allowed to attack first on Shabbos if the Nochrim only want money. If the Nochrim want to kill them, or the Nochrim are attacking a border city, it is permitted to attack first even if the Nochrim only want money.
4. The Gemara concludes that he in fact was asking whether he would be successful in this war.
5. Rebbi Meir says that he does not have the Techum of the city, since he did not intend that the city should be his residence, and therefore he has only 2,000 Amos in each direction. Rebbi Yehudah says that since he indeed was within the Techum of the city when Shabbos arrived, he has the same Techum as a resident of the city.
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