Question: Where (according to the Rabanan) would we place the Tefach constituting the third wall?

Answer (Rav): The Tefach is placed at a right angle, at either end of the "L" created by the first two walls.

Question (R. Kahana and R. Asi): It should be placed at an angle (45 degrees) into the "L" (giving the appearance of closing the Sukah)!?

Answer: Rav was silent (indicating his non-acceptance - Ritva).

Levi was cited (by Shmuel) as ruling like Rav.

Answer (R. Simon, or, R. Yehoshua b. Levi): The Tefach is a generous Tefach and it is placed just under three Tefachim from the end of the L (making a Lavud wall of four Tefachim, the majority of a seven-Tefach wall).

(R. Yehudah): The Sukah is Kosher if made from two parallel walls (like a Mavoy Mefulash) with the additional Tefach placed at any end.

(R. Simon, or, R. Yehoshua b. Levi): Such a Sukah requires a board slightly larger than four Tefachim, placed within three Tefachim of the end of one of the parallel walls.

Question: Why, when the walls were perpendicular, a generous Tefach was sufficient, and now you require four Tefachim?

Answer: The perpendicular walls create two proper walls (and the small addition is sufficient), whereas parallel walls are not Kosher, and Rov Dofen is needed to be Machshir.

(Rava-First Rendition): The additional Tefach must be placed in the form of a Tzuras ha'Pesach (a half-Tefach board on each end of a seven-Tefach-wide Tzuras ha'Pesach, connected above -Rashi D"H Amar Rava).

(Rava-Second Rendition): A substitute for the additional Tefach could be a seven-Tefach-wide Tzuras ha'Pesach, even without a total of a Tefach-width.

(Rava-Third Rendition): In addition to the Tefach, we require a seven-Tefach-wide Tzuras ha'Pesach.

R. Kehana made a Sukah using a generous Tefach within three Tefachim, in addition to a Tzuras ha'Pesach.

Question (R. Ashi): But Rava said that either a Tefach or a Tzuras ha'Pesach will suffice!?

Answer (R. Kehana): I hold like the third rendition of Rava.

(Rabah or Rava): Since (Migo) we see the additional Tefach as constituting a wall for Sukah, it would also be considered a wall for the purposes of carrying on Shabbos.

Question (Abaye): But the Beraisa teaches that the Halachos of Shabbos during Sukos are more Chamur than the Halachos of Sukah the rest of the week!?

The Beraisa says that walls are created for Sukah the same way that they are created for Shabbos.

A Lavud wall (made of reeds with less than a three- Tefach space in between) is thus Kosher.

Shabbos has the Chumrah that we require that the Omed exceed the Parutz, which we do not require for Sukah (since we allow the absence of all of the fourth and most of the third walls).

We see that we not not call any Kosher Sukah as enclosed for the purposes of the Shabbos of Sukos!?

Answer: The Beraisa means that Shabbasos other than the Shabbos of Sukos have this Chumrah.

Question: Then the Beraisa should have listed a Chumrah of the general Hilchos Sukah over the Sukah of Shabbos in that a Sukah requires a generous Tefach as a third wall whereas you (if Abaye is speaking with Rava, but Mar, if it is Abaye speaking to his Rebbi, Rabah) only require a Lechi, and not a Tefach, at the opening of the Mavoy Mefulash!?

Answer: It is unnecessary to point that out since we already apply the Migo to permit a Sukah wall on Shabbos, it goes without saying that we permit a Sukah owing to its validity on Shabbos.

Rabah (or Rava): also taught that we could put Sechach on the four posts around a public well (Pasei Bira'os).

Each of these Halachos are needed:

Had we been taught only the Hechsher of a Lechi-equipped Mavoy we might have attributed the Heter to the presence of two proper (though parallel) walls, but not applied the Heter where there are no actual walls.

Had we been taught only Pasei Bira'os we might have attributed the Heter to the existence of four walls (albeit only Halachic ones) and not applied the Heter where we do not call it a four-walled enclosure.

Had we been taught both of these, but not the blanket rule above that anything which constitutes a wall for Sukah is deemed a wall for Shabbos, we might only have applied the Heter from Shabbos (which is more Chamur) to Sukah, and not the reverse.

Beraisa (Rabanan): If the light that comes in through the walls (such as through gaps or windows) is more than the shade, the Sukah is Kosher; the Sukah is Pasul only when the light coming through the Sechach is more than the shade.

(R. Yoshiyah) Even light coming through the sides will invalidate the Sukah.

Question: What is R. Yoshiyah's reason?

Answer: It is written, "You shall cover (v'Sachosa) the Aron with the Paroches."

The Paroches is a partition and yet the Torah calls it "Sechach."

Therefore, the partition must be like the Sechach (and not let more light than shade into the Sukah).

Question: How do the Rabanan respond?

Answer: The Torah calls the Paroches "Sechach" because its edges extended slightly over the side of the Aron and had the appearance of Sechach.

(Abaye): Rebbi, R. Yoshiyah, R. Yehudah, R. Shimon, R. Gamliel, Beis Shamai, R. Eliezer, and Acherim all hold that a Sukah must be a Diras Keva.

Rebbi says (Beraisa) that any Sukah which is not 4x4 Amos is Pasul.

R. Yoshiyah, as we learned above (in the Beraisa, 1.a.)

R. Yehudah says (Mishnah) that a Sukah taller than 20 Amos is Kosher.

R. Shimon says (Beraisa) that three of the Sukah's walls must be of proper size, but the fourth may be even one Tefach wide.

R. Gamliel says (Beraisa) that a Sukah made atop a wagon or a boat is Pasul.

Beis Shamai says (Beraisa) that one whose head and most of his body were in the Sukah but his table was in the house did not fulfill the Mitzvah.

R. Eliezer says (Mishnah) that a Sukah made like a tent (the roof of which also serves as the walls) or a Sukah made by leaning the branches of the Sechach against a wall (forming a shelter underneath) is Pasul, because it has no actual roof.

Acherim say (Beraisa) that a Sukah made like a bird coop (i.e. round) is Pasul, because it does not have corners.