Rif Eruvin 30b {Eruvin 92b continues ... 94a}

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30b

{Eruvin 92b continues}
the large is permitted and the small is prohibited. A large courtyard that is breached into a small - the large is permitted and the small is prohibited because it is as a doorway of the large.

{Eruvin 93b}
Gemara:
Mereimar expounded: An embankment of 5 handbreadths and a partition on top of it of five handbreadths combine.
And so is the halacha.

Rav Oshaya inquired: Do tenants who arrive on Shabbat impose restrictions?
Rav Chanania said: Come and hear: A large courtyard that was breached to a small {courtyard}, the larger is permitted and the smaller is forbidden. {And the assumption is that this breaching happened on Shabbat, and so the residents of the larger courtyard are equal to tenants who arrive on Shabbat.}
Rabba said: Say that it was breached while it was yet day {on Friday}.
Abaye said to him: Master {=Rabba} should not say "say" {which implies "perhaps" one might say this}, but rather certainly it was breached while it was yet day. For it was Master himself who said, 'I inquired of Rav Huna and I inquired of Rav Chisda {our gemara: Yehuda} regarding where they made the eruv relying on a certain door and the door was blocked up; if they made the eruv relying on a certain window and the window was blocked up; what is the law?' And they said to me: Shabbat, once part of it is permitted, all of it is permitted.'"

It was stated {by Amoraim}:
If a wall between two courtyards collapsed:
Rav said: We may only move objects in it within four cubits.
And Shmuel said: {Eruvin 94a} This one may move his objects to the very foundation of the wall, and this one {from the courtyard on the other side} may move his objects to the very foundation of the wall.

Shmuel and Rav were dwelling in a certain courtyard when a parting wall collapsed.
Shmuel said to them: Take a cloak and spread it across.
Rav turned away his face {as a mark of displeasure}.
Shmuel said: If Abba {=Rav} objects, take his girdle and tie {the cloak in place} with it. {That is, I disregard his objection.}

How could Shmuel have done this? {He should not have required any new partition at all, even one made by a cloak.} He is the one who says that this one may move objects up to the very foundation of the wall and this one {from the other courtyard} may move objects up to the very foundation of the wall!
Shmuel only did this for the sake of privacy.
Rav, if he felt that it was forbidden, should have said that it was forbidden!
It was Shmuel's place {and under Shmuel's jurisdiction}. If so, why did he turn away his face?
In order that they should not say that he retracted his opinion {that it was forbidden}.

And the halacha is like Shmuel, for we have established that tenants who come on Shabbat do not impose restrictions; Since part of it {=Shabbat} was permitted, all of it is permitted.

Mishna:
A courtyard that is breached to the public domain - if a person carries in from it into the private domain or from the private domain into it, he is lable. These are the words of Rabbi Eliezer.
And the Sages say: From it into the public domain, or from the public domain to within it - he is exempt, because it is as a karmelit.