Rif Eruvin 1b {Eruvin 5a continues ... 6a}

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1b

{Eruvin 5a continues}
It was stated in Rav Ami and Rav Asi's name: if there is a post {pas} of 4 {Chavot Yair adds: handbreads}, it permits a gap up to ten {cubits}. And if not {=there is no pas}, then {a gap of} less than 3 handbreadths is permitted {for we may employ lavud to bridge to gap}, 3 handbreads {+} is not permitted.

And we establish this of Rav Ami and Rav Asi as referring to a case when there is a boundary - that is, in the place of the breach, there is still a boundary {from the stubble of the walls} like an enclosure holds back the members of the public domain {from easily entering}.

Rami bar Abba cited Rav Huna: A lechi {= a vertical post erected at the entrance to an alleyway. it is an alternative to the horizontal korah} which juts our from the wall of the alleyway less than four cubits is reckoned a lechi and does not need another lechi to come and permit it. {If it juts out} four cubits, it is reckoned an alleyway and needs another lechi in order to permit it.

As regards the {preceding} segment, I have seen two explanations which were not exact, for there are refutations to them, and therefore I have not written them {here}. And here is the {true} explanation:

A lechi which juts out of the wall of the alleyway such that there is {now} a fourth wall extending across the width of the alleyway, then if it only extends less than 4 cubits it is judged to be a lechi since it is not the {minimum} length of an alleyway {that is, 4 cubits}. Therefore the alleyway does not require another lechi to permit it. And if there is in it {the lechi} the {minimum} measure of an alleyway {=4 cubits}, it is not judged to be a lechi but rather as the other walls of the alleyway, and the entrance to the alleyway thus remains without a lechi, and therefore requires a lechi to permit it. And that {additional} lechi, we may place it on the opposite side, or else he may place it next to the first one {lechi}
and {if he places it next to the first lechi} add a bit {to the new lechi} over the thickness of the first one, or reduce a bit from the thickness of the first one, such that it is a heker {so people recognize it as different than the wall and it reminds them of the boundary into a new domain}.

{Eruvin 5b}
Rav Huna the son of Rav Yehoshua said: They only said this as regards an alleyway whose width was eight cubits, such that on this fourth wall {= the open end of the alleyway marked by the long, 4 cubit lechi}, the breach in it is equal to the standing {wall} in it. For {then,} the standing is 4 {cubits} and the breach is 4 {cubits}. But by an alleyway whose width in 7 cubits, since the standing is 4 cubits and the breach is 3 {cubits}, it is permitted by the fact that the standing portion is greater than the breach {omed merubeh al haparutz, and this may be learned} via a kal vachomer from a courtyard. A courtyard which is not permitted via a lechi or a korah but rather only with strip of four {handbreadths = pas daled} is permitted via the standing portion being greater than the breach, and does not need a strip {pas}, then surely an alleyway which is permitted via a lechi or a korah should permitted via the standing portion being greater than the breach, and would not need a lechi.

And Rav Ashi came and said that even as regards an alleyway of width 8 {cubits exactly} you do not need a {new} lechi {if your first lechi was 4 cubits across}. For what have you? {Firstly, it is not clear than these measures are exact, to the level of the atom.} If the standing portion is slightly more {than 4 cubits, i.e. the lechi = standing portion is 4.00001 cubits, and the breach is 3.99999 cubits}, then it is permitted because the standing is greater than the breach. And if the breach is slightly more {than 4 cubits, i.e. the breach is 4.00001 cubits, and the lechi is 3.99999 cubits}, since there is not in the jutting out portion {=the lechi} a length of 4 {cubits}, it is judged to be a lechi {and not just a wall}. What will you say? That they are exactly equal {, both 4.0 cubits}? This is a case of doubt in a Rabbinic matter {for the need for a lechi is Rabbinic}, and in a Rabbinic doubt we rule leniently.

And the halacha is like Rav Ashi. This is the interpretation of this segment - it is a clear and insightful explanation, and there is not in it any difficulty or doubt.

It was stated: A twisted alleyway {aqum - where each alleyway entrance leads to the public domain}:
Rav said: Its law is like that of an open alleyway. {i.e. a straight alleyway whose two entrances lead to the public domain}
And Shmuel said: Its law is like that of a closed alleyway {i.e. a straight alleyway with only one entrance leading to the public domain}, and it is permitted via a lechi or a korah {at the end leading to the public domain.}

{The same is true at each leg of the crooked alley that it needs a lechi or korah, Shmuel is only addressing one leg of this crooked alleyway, which may be permitted via a lechi or korah at the entrance to the public domain, without any regard whatsoever as to what is done with the second leg, for the right angle separates these two "closed" alleyways.}