Eruvin 57B

הא מני ⁠— רבי מאיר היא.

In accordance with whose opinion is this clause of the Mishnah? It is the opinion of R' Meir, who maintains that one allocates a karpef to each city.

אי רבי מאיר היא, הא תני ליה רישא: נותנין קרפף לעיר, דברי רבי מאיר?

The Talmud continues to ask: If it is in accordance with the opinion of R' Meir, didn’t we already learn in the first clause: One allocates a karpef to each city; this is the statement of R' Meir? What need is there to mention R' Meir’s opinion again?

צריכא, דאי מההיא, הוה אמינא: חד לחדא, וחד לתרתי. קא משמע לן דלתרתי תרי יהבינן להו.

The Talmud answers: It was necessary to mention his opinion again, as, if we had learned his opinion only from that first clause, I might have said that one allocates one karpef for one city and also one karpef for two cities. Therefore, the Mishnah teaches us that for two cities, one allocates two karpef areas.

ואי אשמעינן הכא, משום דדחיקא תשמישתייהו, אבל התם דלא דחיקא תשמישתייהו, אימא לא, צריכא.

And conversely, if the Mishnah had taught us this law only here, with regard to two cities, one might have said that only in that case is each city granted a separate karpef, because a smaller space between the two adjacent cities would be too crowded for the use of both cities. But there, with regard to one city, where the area of the city itself is not too crowded for the use of its residents, one might say that it is not given any karpef whatsoever. Therefore, it was necessary for the Mishnah to teach both clauses.

תנן: וכן שלשה כפרים המשולשין, אם יש בין שנים החיצונים מאה וארבעים ואחת אמה ושליש ⁠— עושה אמצעי את שלשתן להיות אחד. טעמא דאיכא אמצעי, הא ליכא אמצעי ⁠— לא. תיובתא דרב הונא!

The Talmud tries again to adduce proof from the Mishnah, in which we learned: And likewise, in the case of 3 villages that are aligned in a row, if there is only 141⅓ cubits separating between the two outer ones, the middle village combines the 3 villages into one. At this point the Talmud understands that the Mishnah here is dealing with 3 villages arranged in a straight line. Therefore, it makes the following inference: The reason that the 3 villages are considered as one is only because there is a middle village, but were there no middle village, they would not be considered as one. This appears to be a conclusive refutation of the opinion of Rav Huna. According to Rav Huna, the two villages should be considered as one even without the middle village, due to the double karpef.