(Mishnah): A beam or stone that protrudes more than a tefach from Reuven's wall into Shimon's courtyard can create a chazakah and Shimon can protest it. If it protrudes less than a tefach, it does not create a chazakah and Shimon cannot protest it.

(Gemara) - R. Ila citing R. Yanai: If a person has a chazakah to have a protrusion of a tefach, he is permitted to widen the protrusion as much as its length.

Question: How much can he extend the protrusion outwards?

Answer (Nasan b'R. Hoshiya): Like the protrusion made when two people wish to make a sign to delineate between two houses.

(Mishnah): A person should not open his windows (even) into a shared courtyard.

If one of the partners bought a house in another courtyard, he should not open it into the shared courtyard (as he increasing the flow of people using that courtyard as the residents of that new house will also use it).

If he built an attic on his house, he should not open it to a shared courtyard. Rather, if he wishes, he can build a room within his house or build an attic on top of his house and open it into his house. (Adding residents within his own home, thereby adding to the number of people using the courtyard is certainly permitted.)

A person should not make an opening opposite a pre-existing opening or a window opposite a window.

If it was a small opening or window, he should not make it larger; if there was one, he should not make a second one.

But he can make an opening opposite a pre-existing opening or a window opposite a window in a public domain.

In a public domain, if it was small, he can make it larger; if there was one, he can make a second one.

(Gemara) - question: Here (in a Beraisa) you say that an opening opposite an opening is permitted; but here you said that it is prohibited?

Answer: It is permitted in a mavoi (alleyway); it is prohibited in a shared courtyard.

Question (Beraisa): Just as the courtyard members are able to protest each other's use of the courtyard, so mavoi members should be able to protest each other's use of the mavoi?

Answer #1 (R. Ila): For a mavoi, if they gave him permission to open it, they can no longer protest; for a shared courtyard, even if they gave him permission, they can still protest, as the hezek re'iyah is worse there (since people are not expecting others to look).

Answer #2 (R. Yochanan): (The Beraisa was discussing a mavoi that contains a vegetable garden.) Gardens are different, since they sprout. (Although in a regular mavoi, it is expected that people will build; if it contains a vegetable garden, building there is discouraged as it will disturb the beauty of the place. Therefore it is prohibited there to make an opening opposite an opening, as in the case of a shared courtyard.) (Note: The Meichal Mayim, written by the Aruch HaShulchan, corrected the text here and said that the Ramban does the same.)

Question (R. Nasa): If so, one should say the same thing for a destroyed house and prevent a person from building there since it disturbs the aesthetics of the place!

Beraisa taught in Bavel (R. Yaakov bar Acha): If a person makes a window of four amos in the wall of his courtyard (that separates his courtyard from his neighbor's) in the presence of his neighbor, as soon as he makes it, his neighbor can close it up.

Question: If the neighbor stood there and did not protest, how can he later close it up?

Answer: The neighbor can say, "I was only silent because I wanted to watch you work for nothing as I will require you to close it up".

If the neighbor handed him stones as he built, he could still claim, "I was pretending to help him in order to poke fun at him".

Beraisa (also taught in Maseches Ohalos): (The Mishnah earlier - see 58-1 (c)(d) - taught that small window does not create a chazakah. This is because it is insignificant and useless; but a large window can create a chazakah since it has a use, such as for transferring items. However, if it is used for light, even if it is small, it can create a chazakah. The Beraisa in Maseches Ohalos teaches that) if a person built five concentric walls, each with a window that lines up with the others, clearly his intent is that light should come in. Therefore, even if the windows were only the size of a drill hole, they transfer tumah through them. But if the windows did not line up, he built them for use rather than light and they do not transfer tumah unless they are a tefach wide. (Note: This entry and the next one should more correctly be positioned after Mishnah 8 that teaches the law of windows. The Ramban writes that the explanation of this Gemara is unclear.)

This, that the Beraisa rules that the transferal of tumah depends on his intent when he built the windows, supports that which the builders say - a window that opens into a covered porch, since it can only bring in a minimal amount of light, it does not create a chazakah because it does not bring tumah through it (and the Gemara is teaching that the same rule that applies to tumah applies to chazakah).