Rif Succah 3a {Succah 7b}

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3a

{Succah 7b}
Rava {Bach emends to Rabba} said: If one places sechach atop an alleyway which has a lechi {a vertical post of any width whatsoever placed at the opening of the alleyway to the public domain to serve as a reminder of the transition}, it is valid.

And Rava {Bach emends to Rabba} said:If one places sechach atop pasei biraot {strips around wells - see relevant halachot in Eruvin 17b} it is valid.

For since it is a wall in terms of Shabbat, it is a wall in terms of Succah.

And both are needed. For if we had been informed of the alleyway which had a lechi, this is because it has two perfectly fine walls. But the case of pasi biraot, which does not have two walls, I would say no. Therefore it is needed.

And if we had been informed on pasei biraot - there, there are four walls, but by an alleyway that has a lechi, which does not have four walls, I would say no. Therefore it is needed.

"And that {succah} whose sun is greater than its shade is invalid":
The Sages learnt {in a brayta}: The sun coming through the sechach and not through the walls {will invalidate it}.
Rabbi Yoshiya said: Even because of the walls.

Abaye said: Rabbi Yoshiya, Rabbi, Rabbi Yehuda, Rabbi Shimon, Rabban Gamliel, Bet Shammai, Rabbi Eliezer, and Others all maintain