1)

(a)Initially, we establish the Beraisa which forbids putting up a Mechitzah of people, animals or vessels on Shabbos, standing up a bed and draping a sheet over it to protect a corpse or food from the rays of the sun - like Rebbi Eliezer, who forbids re-placing a skylight (a temporary Mechitzah) on Shabbos and Yom-Tov; whereas Rav Nachman who permits making a Mechitzah, holds like the Rabbanan, who permit it.

(b)Rav Nachman has support for this from a Beraisa - which permits the placing of people to form a wall for one's Sukah, enabling one to eat etc. in the Sukah, and to put up temporary walls as protection (in the same way as the previous Beraisa forbade it).

(c)The Gemara rejects this explanation - on the grounds that the Rabbanan of Rebbi Eliezer only permit adding to an existing Mechitzah, but not putting up a fresh one.

2)

(a)Rebbi Meir forbids the use of an animal as the wall for one's Sukah, (because it may run away). Since it is not considered a wall, there is no harm in placing it there (where it will serve as an Ohel - but not as a Mechitzah). Note: The Gemara could have refuted this suggestion by pointing out that the Beraisa (which we just established like Rebbi Meir), permits eating and drinking etc. in the Sukah - suggesting that the animal has the full Din of a Mechitzah. It is also not clear whether this answer satisfactorily answers Rav Nachman (see Tosfos and Ritva).

(b)Rebbi Meir only invalidates an animal that is placed as a wall, because it may run away, but who says that he also invalidates a person or vessels (which the Beraisa with regard to Sukah also permits)?

(c)In addition, asks the Gemara, even if we establish the second Beraisa like Rebbi Meir - he can only be following the opinion of the Rabbanan of Rebbi Eliezer (since Rebbi Eliezer forbids even to add to an existing wall), and the Rabbanan permit only adding to an existing wall, but not putting one up from scratch, as we asked earlier.

3)

(a)The Beraisa which permits putting up a wall of vessels - is speaking about a Sukah which already has three Kasher walls, so that the fourth wall of vessels is nothing more than an addition, which the Chachamim permit. Whereas the Beraisa which forbids it, speaks about a Sukah with only two walls, in which case, adding a third wall of vessels will render the Sukah Kasher, and this the Rabbanan do not permit.

(b)The proof for this is from the Lashon 'Nafal Dofnah' (implying one of the walls which rendered the Sukah Kasher) used by the first Beraisa, which forbids using an animal - whereas the second Beraisa simply says 'Oseh Adam es Chavero Dofen' (which could just as well apply to the fourth wall of the Sukah, which explains why it is Kasher).

4)

(a)The Beraisa which permits making a wall of people to enable one to eat, drink or sleep in one's Sukah - speaks when they are placed there without prior knowledge that they have been placed as a Mechitzah; whereas the Beraisa which forbids it, speaks when they know why they are there.

(b)Rav Chisda, who knew that the people were needed to form a Mechitzah - did not actually form part of it.

(c)We cannot answer the discrepancy in a. by establishing the Beraisa which permits it by the fourth wall - because with regard to a Mechitzah of people, the Beraisa specifically mentions that it comes to permit eating, drinking and sleeping in the Sukah - which can only be referring to the third wall, which renders the Sukah Kasher, and not to the fourth one, as we explained earlier.

5)

(a)Shmuel gave lashes to those men who served as a Mechitzah (to enable water to be brought in from the street), because they did so with the knowledge that they were standing there as a Mechitzah.

(b)Some flasks belonging to Rava were lying in the street on Shabbos, so the Shames took advantage of the throngs of people who came to hear his Derashah to carry them into the house, using the people as Mechitzos. When this happened a second time, and his Shames wanted to bring them in again, Rava stopped him - because if people are used as Mechitzos too many times, it is inevitable that eventually, they will realize why they are there, and we have already learnt that people may only be used as Mechitzos as long as they are not aware that they are being used as Mechitzos.

6)

(a)Someone who left his Techum legally, only to discover that his journey was unnecessary (for example if he left to testify that he had seen the new moon, and then discovered that his testimony was not needed) - has two thousand Amos from where he is, when he makes the discovery.

(b)Someone who leaves the Techum Shabbos to save his property from robbers or from a river that was threatening to overflow and swamp his field, or a midwife who left to deliver a baby - are all included in the term 'legally'.

7)

(a)Rabah explains 'Im Hayah be'Soch ha'Techum, Ke'ilu Lo Yatza' - to mean that if he was still within his original Techum, he is permitted to return to his house, and to revert to his original Techum, as if he had not left his house in the first place.

(b)We might otherwise have explained it to mean that, once he left his house, he has given up his original Techum, which now leaves him with no Techum at all.

(c)Rav Shimi bar Chiya explains the Mishnah to mean - that, even if he has left his original Techum, he is permitted to go back etc., provided his current Techum overlaps his original one.

(d)Rabah holds that, once he leaves his Techum, he acquires Shevisah in his new location, and we would not say in such a case that it is as if he had not left his Techum. Nor does Rabah hold of the Neherda'i, who said earlier (41b) that, once he re-enters his original Techum, he reverts to it.

8)

(a)According to Rashi's second explanation - even Rabah speaks when he has left his Techum; however, according to him, it is as if he had not left his house, and he reverts to his original Techum, whereas according to Rav Shimi bar Chiya, since the two Techumin overlap, they become like one Techum, giving him a new Techum of almost eight thousand Amos, incorporating his original two thousand Amos to the East of his original residence (for example), and two thousand Amos to the west of his new one.

(b)Abaye asks Rabah from someone who acquired his residence in a cave of four thousand Amos, whose roof was less than three thousand Amos, and which had two entrances (like most caves did), one at either end of the roof - did he not agree, he asked him, that one was able to walk the entire three thousand Amos of the roof, plus two thousand Amos from the one end of the roof, and two thousand Amos from the other, from which we see that when two Techumin overlap, they do merge into one (like Rav Shimi bar Chiya maintains).

(c)There is no proof from there, Rabah counters - because that speaks when he acquired his residence before Shabbos, which is why he acquires both Techumin simultaneously; whereas in our case, when he only acquired the one Techum before Shabbos entered, he cannot acquire the second Techum on Shabbos, to combine with the first, only (if and when he does acquire it) independently - at the expense of his original Techum.

9)

(a)Abaye eventually proves Rabah wrong from Rebbi Eliezer, who (in a Mishnah later in the Masechta) permits someone who left his Techum on Shabbos to return, provided he is not more than two Amos outside the Techum. - Now, he had not acquired those two Amos before Shabbos (as Rabah considers necessary for one Techum to be absorbed inside another. Nevertheless, Rebbi Eliezer considers the two Techumin that are outside his original Techum to be absorbed in his original Techum - as if they were one Techum - like Rav Shimi bar Chiya.

(b)Nor can Rabah answer that that is the opinion of Rebbi Eliezer, but the Rabbanan argue (and he will hold like the Rabbanan) - because the Rabbanan only argue about re-entering for a D'var Reshus, but for a Devar Mitzvah, they agree with Rebbi Eliezer that one is permitted to return from the two Amos outside the Techum.