1) DESECRATING SHABBOS IN ORDER TO DEFEND A JEWISH CITY
QUESTION: The Gemara cites a Beraisa which states that if Nochrim attack a Jewish city in order to loot and rob it, we may not desecrate Shabbos to defend it since there is no concern that Jewish life will be lost (Piku'ach Nefesh). However, if that city is on the border of a larger Jewish area, then it is permitted to desecrate Shabbos in order to protect the city, even if the Nochrim who attack it intend only to rob it. Even though their objective is to steal the money of the Jews, we fear that they might conquer the entire city and obtain a stronghold from which to conquer further Jewish towns, thus creating a concern for Piku'ach Nefesh. Rav Nachman adds that Neharde'a in Bavel is considered a border town. RASHI explains that Neharde'a was on the border between Jewish towns and non-Jewish towns.
What is Rav Nachman telling us when he says that Neharde'a is "considered" a border town? It is a border town!
ANSWER: The TORAS CHAIM suggests a different explanation for the words of Rav Nachman and explains that Neharde'a was not on the border. He quotes the HAGAHOS ASHIRI who writes that outside of Eretz Yisrael, Jews may desecrate Shabbos in order to defend any city attacked by Nochrim, even if the city is not on the border of a larger Jewish area, and even if the Nochrim come only for money. This is because the Jews outside of Eretz Yisrael live among the Nochrim, and thus every Jewish town is like a town next to a border; a town conquered by Nochrim would pose a significant threat to the Jewish populace. The Toras Chaim explains that this is what Rav Nachman here is teaching. Since Neharde'a in Bavel is situated among the Nochrim, the Halachah that applies to border towns applies to it as well, even though it is in the middle of a country.
Perhaps this is Rashi's intention as well. Rashi means that we might have assumed that only when the Jewish city is on the border of a country is there a concern that Nochrim who overtake it will attempt to conquer the entire country, in order to build for themselves a more powerful nation. Therefore, such a situation involves Piku'ach Nefesh. Rav Nachman adds that even when the city is in the middle of a country, but it borders on a Jewish section of the country, there is a concern that the Nochrim will decide not only to steal the money of the Jews, but also to torment and persecute the Jews, and therefore the Jews must defend themselves.

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2) THE DIFFERENCE BETWEEN AN OBJECT THAT HAS NO "MAKOM SHEVISAH" AND A MAN WHO HAS NO "MAKOM SHEVISAH"
QUESTION: The Chachamim maintain that an ownerless object is not Koneh Shevisah in its place. Since an ownerless object is not Koneh Shevisah, it may be moved as far as the person (who finds it and picks it up) may walk.
However, the Gemara explains that a person who is not Koneh Shevisah may not walk at all beyond his place (four Amos). Why is a man who is not Koneh Shevisah severely restricted in how far he may walk, while an object that is not Koneh Shevisah has an unlimited Techum?
ANSWER: An ownerless object has no Techum, and therefore it becomes subordinate to the person who picks it up and it acquires that person's Techum. A person, however, is subordinate to no one but himself. If he has no Techum, then he remains restricted and does not acquire the Techum of anyone (or anything) else.

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