1)

(a)'Mavoy she'Nifratz mi'Tzido, be'Eser' - means that a breach of up to ten Amos along the length of the Mavoy does not invalidate the Mavoy, provided the first four Tefachim are still intact.

(b)'me'Rosho be'Arba'ah' - means - that if the breach occured in the section of ten Amos set up to rectify the entrance that was twenty Amos wide, then four Tefachim invalidate the Mavoy.

(c)The reason that a breach of four Tefachim is not considered an entrance (when it is at the side) is because people do not usually make their entrances at the side.

(d)When Rav disqualified a Mavoy in Damchari'ah (because of a breach of four Tefachim in one of its side walls) it was because the people of Damchari'ah were Amei ha'Aretz, and were not taking the Mitzvos too seriously, that he felt he needed to be strict with them (because strictly speaking, a breach that is not more than ten Amos does not disqualify the Mavoy) - 'like a person makes a fence around a breached open field, to protect it'.

2)

(a)Each of the two Mavo'os that lead off from the two main roads etc. ...

1. ... has the Din of a Mavoy Mefulash, according to Rav - and requires a Tzuras ha'Pesach at one end (in this case, in the middle) and a Lechi at the other (where it leads out into the main road.

2. ... has the Din of a Mavoy Sasum, according to Shmuel - and requires no more than a Lechi at the entrance to the main road.

(b)If the Mavoy would be more than ten Amos wide - how could Shmuel consider it to be Sasum.

(c)Consequently, Rav and Shmuel must be speaking about Mavo'os that are ten Amos wide and no more - so we see that, according to Rav, a breach that is not more than ten Amos, is considered a breach (which means that a breach of four Tefachim - the alternative to more than ten Amos - is a breach, like Rav Huna).

(d)Rav Chanin bar Rava rejects Rav Huna's proof - on the grounds that that case is worse, because the public from the two streets use the Mavoy to get from one main road to the other; therefore it loses its status of Mavoy already with a breach of four Tefachim.

3)

(a)Rav Huna, who disqualifies even a breach of four Tefachim when it is not accessible to the people from the street - will agree that, in Rebbi Ami and Rebbi Asi's case (a breach in the side of a Mavoy up to ten Amos), a breach of four Tefachim will not invalidate the Mavoy, because there at least, there are walls on either side of the breach, whereas the breach in the Mavoy Mefulash is completely open, with no walls at the side of the breach (so a breach four Tefachim is considered a breach).

4)

(a)A Reshus ha'Rabim, according to Rashi, must be sixteen Amos wide, must belong to a town with at least six hundred thousand inhabitants, which is not surrounded by a wall, and the street must run straight through it from one gate of the city to the other. (See also Amud 2, answer to 6a).

(b)

1. According to Beis Shamai - a Reshus ha'Rabim requires a door (which is kept closed) at either end.

2. According to Beis Hillel - it requires a door at one end and a Lechi or a Koreh at the other.

(c)The Gemara concludes that the Machlokes Tana'im currently under discussion - is not referring to a Reshus ha'Rabim (which requires a wall around it before it can be permitted), but about Mavo'os which open into them.

5)

(a)When Rebbi says: 'Mi she'Hayah Shnei Batim mi'Shnei Tzidei Reshus ha'Rabim' etc. - he is teaching us that someone who owns two houses, one on either side of the street, is permitted to carry in that section of the street by placing a Lechi or a Koreh at each end.

(b)Before that, Rebbi Yehudah was talking about someone who built a bridge across the street from the house on one side of the street to the house on the other. He is permitted, says Rebbi Yehudah, to carry underneath the bridge, because 'Pi Tikrah Yored ve'Sosem' - meaning that the side of the bridge that is ninety degrees to the ground, extends to the ground (on both sides of the bridge), to form two Halachic walls adjacent to the walls of his house, thereby forming a Reshus ha'Yachid of four walls in the middle of the Reshus ha'Rabim.

(c)The Rabbanan said to Rebbi Yehudah - that one cannot be Me'arev a Reshus ha'Rabim in this manner.

(d)We know that the Rabbanan were not just disqualifying a Reshus ha'Rabim that is rectified in this way, but permitting a Reshus ha'Rabim by means of a door at one end and a Lechi or a Koreh at the other (like Beis Hillel) due to similar statements by Rabah bar bar Chanah and Ula. Rabah bar bar Chanah Amar Rebbi Yochanan said - that if not for the fact that the doors of Yerushalayim were shut at night-time, it would have a Din of a Reshus ha'Rabim ...

(e)... a proof that a Lechi and Koreh will not suffice to permit carrying in a Reshus ha'Rabim, and that doors that are closed are required to achieve that.

6)

(a)One was not Chayav for carrying in Yerushalayim on Shabbos - because, besides the specifications mentioned above (in 4a), it had doors which were kept locked at night.

(b)Yerushalayim, like any walled city, had the Din of a Chatzer Me'ureves (provided the doors were closed when not actually being used), and one could carry in it by means of an Eruv Chatzeros.

7)

(a)According to Chananyah in Beis Hillel - the door of the Mavoy does not need to be shut for the Eruv to be effective.

(b)We cannot bring a proof from Neherda'a, whose doors could not be shut due to the large amount of dust that had accumulated - because those doors were permanently stuck - partially open and partially shut.

(c)When Rav Nachman said that they cleared away the dust - he meant to say that they did so in order enable them to be shut.

8)

(a)Regarding the bent Mavoy in Neherda'a ...

1. ... they followed the Chumra of Rav - to consider it a Mavoy Mefulash.

2. ... and the Chumra of Shmuel - who ruled like Chananyah (who requires a door).

(b)We learn from the Pasuk "ve'ha'Kesil ba'Choshech Holech" - that it is foolish to follow the Chumros of both Beis Shamai and Beis Hillel.

(c)Why then, did they follow the Chumra of both Rav and that of Shmuel in Neherda'a?

9)

(a)The Bas-Kol announced 'Halachah ke'Beis-Hillel!'

(b)Yes, both statements could refer to after the Bas-Kol; however, 've'ha'Rotzeh La'asos ke'Beis Shamai, Oseh' - follows the opinion of Rebbi Yehoshua, who maintains 'Ein Mashgichin be'Bas-Kol'.

(c)In its third answer, the Gemara explains that 've'ha'Rotzeh La'asos ke'Beis Shamai, Oseh' - is only an example, and that it pertains to any Machlokes between any other Tana'im or Amora'im except for that of Beis Hillel and Beis Shamai (because of the Bas-Kol).