Rif Eruvin 23b {Eruvin 75a continues ... 75b}

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23b

{Eruvin 75a, Mishna, continues}
the inner one made an eruv and the outer one did not make an eruv – the inner one is permitted and the outer one is prohibited; the outer one and not the inner one – both of them are prohibited.

This one made an eruv for itself and this one for itself – this one is permitted by itself and this one is permitted by itself.
Rabbi Akiva prohibits the outer one, for the treading of the foot {between the alleyway and the inner courtyard} restricts it.
And the Sages say: The treading of the foot does not restrict it.

If one from the outer {courtyard} forgot and did not make an eruv – the inner is permitted and the outer is prohibited;
from the inner and he did not make an eruv – both of them are prohibited.

If they put their eruv in one place, and one forgot, whether from the inner or from the outer, and he did not make an eruv – both of them are prohibited;

and if they {each courtyard} belonged to individuals – they do not need to make an eruv.

Gemara:
Rabbi Avin {our gemara: when Rabin came, he} cited Rabbi Yannai: There is a three way dispute in the matter:
Rabbi Akiva holds that even the foot which is permitted in its place {=its own courtyard} prohibits when not in its own place {=the other courtyard}.
And the latter Sages {=Chachamim} hold that even the foot which is prohibited in its own place does not prohibit not in its place.
And the {anonymous} Tanna of our Mishna who said that "if they made an eruv in the outer one and not the inner one – both of them are prohibited" holds that the foot which is permitted in its
place does not prohibit when not in its place, while the foot which is prohibited in its place prohibits when not in its place.

"If they put their eruv in one place...":
What is meant by "one place?"
Rav Yehuda cited Rav: The outer {courtyard}.
And why is it called "one place?"
The place which is "designated" {=meyachud} to both of them.

{Eruvin 75b}
"and if they {each courtyard} belonged to individuals":
Rav Bibi cited Rav Ada bar Ahava: If they are three, they are prohibited.

To explain: They are only called "individuals" when there are two courtyards and in each courtyard dwells a single person, such that in total there are two. But if there are three courtyards, and in each courtyards dwells a single person, such that in total there are three, they are forbidden.

What is the reason? Since I might describe them as rabbim {=many residents} in the outer {courtyard}, for any three are rabbim, and since three move about in the outermost courtyard, they are rabbim and forbidden.
And Shmuel said: They are always permitted, until there are two in the inner {courtyard} and they did not make an eruv {and one person in the outer courtyard}, in which case they would be forbidden in the outer {courtyard}.

Rabbi Eliezer said: A gentile {who occupied the inner courtyard} is reckoned like rabbim and forbids.
And why does a single Israelite not forbid?