(Mishnah): A Korah must be wide enough to hold half of a three-Tefachim brick;

It suffices for the Korah to be a Tefach wide, to hold a half-brick. (This will be explained.)

(Gemara - R. Ba): It is in order to receive a row of half bricks along its length.

(Beraisa - R. Shimon ben Gamliel): It is in order to receive a row of half bricks along its width. (Since the half bricks are three Tefachim long, the Korah must be two and a half Tefachim wide, so with plaster it is three wide.)

Question: What [else] do they argue about?

Answer (R. Shein): They argue [also] about strength. According to Rabanan, [it must be able to hold] 20 half bricks. According to R. Shimon ben Gamliel, [it must be able to hold] 40 half bricks.

Question: If there are two Koros, this one is a half Tefach [wide], and this one is a half Tefach, how much space can there be in between [and they join]?

Answer #1 (R. Zeira): It is a half Tefach. (Even when the Korah is a Tefach wide, half a Tefach of the hfc sticks out - what is the difference if [the air under the hfc, half of the] half Tefach sticks out on this side and [half of the] half Tefach sticks out on the other side, or if the half Tefach is in the middle?

Answer #2 (R. Hoshayah - Beraisa): A Tefach [may be between them].

If there are two Koros, this is a third [of a Tefach] and Kolshehu, and this is a third and Kolshehu, and between them is less than a third - the law is like what R. Yochanan taught, that the standing wall (Chulyas ha'Bor) and gap in the middle] join to four [to make it Reshus ha'Yachid]. This is if what stands exceeds the gap. (Also here, since the gap is less than the thickness of the Koros, it is like a Korah one Tefach wide, which permits.)

If a Korah comes out from this wall, and does not reach the second wall, or if two Koros [one coming out of each wall] opposite each other, if there are three Tefachim between [a Korah and the wall in the first case, or between the two Koros in the latter case], he needs [another] Korah. If not (there are less than three Tefachim in between), he does not need [another] Korah.

Some teach [that it depends on whether or not the gap is] four Tefachim;

The one who says [that Lavud does not apply to a gap of] three, it is because it is enough for a person to pass through. The one who says [that Lavud does not apply to a gap of] four, it is because it is a significant place. (PNEI MEIR)

If one end of a Korah is above 20 Amos, and the other end is below 20 Amos, we view that if you would cut off within three Tefachim [of the wall on the higher side, and all that remains], is within 20 Amos, it is permitted. If not, it is forbidden.

If one end of a Korah is above 10 Tefachim, and the other end is below 10 Tefachim, we view that if you would cut off within three Tefachim [of the wall on the lower side, all that remains], is above 10 Tefachim, it is permitted. If not, it is forbidden. (We explained this like HA'GAON RAV C. KANIEVSKY, SHLITA.)

If there are two Koros, one above the other [and together they are enough to hold a half brick], R. Yosi bei R. Yehudah says, we view the bottom one as if it were above, and the top one as if it were below, as long as the top is not above 20 Amos and the bottom is not below 10 Tefachim.

Observation: We find that R. Yosi bei R. Yehudah taught like his father, and argues with his father;

He taught like his father - this that he taught we view the bottom one as if it were above, and the top one as if it were below. (Mishnah 1:5 says that if a Korah is made of straw or reeds, we consider it to be of metal. We establish this like R. Yehudah.)

He argues with his father, this that he said as long as the top is not above 20 Amos and the bottom is not below 10 Tefachim. If you would say that he holds like his father, it can even be very high!

(R. Yosi citing R. Chinena bar Shalmiya, and R. Yudan citing R. Chinena bar Shalmiya citing Rav): This is if the top Korah is within three Tefachim of the bottom one. (OHR SOMAYACH, Hilchos Shabbos 17:25 - after lowering the top to the level of the bottom, the horizontal distance between them is less than three.)