(R. Avahu citing R. Chinena citing Kahana): The Halachah does not follow R. Yehudah.

Question: Had he not said so, what would we say? R. Yehudah argues with Chachamim - does the Halachah follow R. Yehudah?!

Answer: Because R. Yakov bar Idi said in the name of R. Yehoshua ben Levi that the Halachah follows the lenient opinion in Hilchos Eruvin, and Rav Yitzchak bar Nachman said in the name of R. Yehoshua ben Levi that the Halachah follows R. Yochanan ben Nuri...

Question: And we challenged [Rav Yitzchak bar Nachman], didn't R. Yakov bar Idi say in the name of R. Yehoshua ben Levi that the Halachah follows the lenient opinion in Hilchos Eruvin? (If so, we already know that R. Yehoshua ben Levi rules like R. Yochanan ben Nuri!)

Answer: We answered that we would have thought that this is when an individual argues with an individual, but [we do not follow the lenient opinion when it is] an individual against Chachamim. Rav Yitzchak bar Nachman came and said in the name of R. Yehoshua ben Levi that the Halachah follows R. Yochanan ben Nuri, even though Chachamim argue with him;

Summation of Answer (c): Here, [we could have thought that] the Halachah follows R. Yehudah, even though Chachamim argue with him. Therefore, he needed to teach that the Halachah does not follow R. Yehudah.

(Shmuel): The Halachah follows the lenient opinion in Eruvin.

Question (R. Chiya bar Ashi): Does this apply to the Mishnah - bridges [whose sides descend and make walls] Mefulashim, one may carry under them on Shabbos. R. Yehudah says so. Chachamim forbid?

Answer (Shmuel): No - I said that [the Halachah follows the lenient opinion] in Eruvin, but not in walls.

Kahana holds like this teaching of Shmuel. (Therefore, he ruled unlike R. Yehudah, for they argue about a wall. We explained this like SEFER NIR.)

Inference: [The Mishnah obligates lowering] only if it is above 20. This implies that if it is at the end of 20 (the bottom of the Korah is exactly 20 Amos high), it is Kosher.

This is like Rav, for Rav said that what is at the limit of the Shi'ur, we are lenient.

Rav said that if one slaughtered half [the Simanim], it is Kosher. (We explained this like HAGAHOS R. DINAR.)

(R. Yochanan): What is at the limit of the Shi'ur, we are stringent.

(R. Chiya citing R. Yochanan): A Mavuy whose Korah is above 20, he puts [the bottom of] the Korah within 20, and diminishes [the gap] within 20.

(R. Yosah): This is if the entire Hechsher Korah is within 20 (the part below 20 would be a Kosher Korah by itself).

(R. Chilkiyah citing R. Acha): [Our Mishnah can] even be like R. Yochanan;

Why did [R. Yochanan] say that [if none of the Korah is within 20] it is Pasul? It is because if you say that he may put within (i.e. at the end of) 20, he will come to put above 20.