Question: This is difficult. Why is his Eruv valid? It is a Karmelis since it is four Tefachim wide, and it is forbidden to carry to the public domain!

Answer #1: A vessel cannot be a Karmelis, as Rashi explained earlier (8a) regarding his box being placed etc.

Answer #2: Alternatively, this is according to Rebbi who says that anything that is due to a Rabbinic prohibition was not decreed during twilight.

Observation: Since Rav Papa gives this answer, the implication is that he holds that one can use the sides of the trees. Rav Ashi implies later that this is forbidden, as he says, "Now that we say that the sides may not be used etc."

Question: I have a difficulty, as in Chagigah (17a) they seem to have the exact opposite opinions (regarding using the sides of an animal)! Rav Papa says that we see from this that the sides of an animal are forbidden, as if one would think they are permitted, we should permit Semichah on the head of a sacrifice on Shabbos as its head is considered like its sides! Rav Ashi says even if we say that the sides are permitted, anything that is equal to the height of its back is like its back, and therefore would be forbidden.

Question: Rebbi asks, why isn't this one of the cases listed in "Ya'al Kegam," meaning the cases where we rule like Abaye (as stated in Bava Metzia (22b)? This is as Rava states that the one who forbids using the sides also forbids using the sides of the sides, while Abaye says that everyone agrees that the sides are forbidden, and only argue regarding the sides of the sides (and the Gemara clearly rules like Abaye).

Explanation #1: Rashi explains that undoing the bundles is like making food (for the animal).

Observation: It must be that Rav Yehudah and Rav Huna also argue regarding the following (see Bach). Rav Yehudah considers undoing the bundles as making food, while Rav Huna does not consider it making food.

Question: Rabeinu Tam has difficulty understanding that this is a distinction between Rav Yehudah and Rav Huna.

Explanation #2: Rather, they both that undoing the bundles is unlike making it into food or going through too much trouble to make it into food, as this cannot be considered trouble. This is why they both permit it.

Implied Question: The Gemara in Eruvin (20b) states that a camel whose head and most of his body are inside can be force fed from the inside. (This implies force feeding a camel is permitted on Shabbos!)

Answer: The force feeding referred to in Eruvin (ibid.) is not the same type of force feeding that we say here is forbidden on Shabbos. Rather, it is referring to a lesser type of force feeding that our Mishnah states is permitted (and there is an argument in our Gemara regarding the exact difference between the two). This is the explanation of Rabeinu Shmuel.

Observation: I explained this earlier (18a).