Rif Eruvin 13b {Eruvin 48a continues ... 49b}

HIDE/SHOW IMAGE
13b

{Eruvin 48a continues}
and these for cubits we grant him using his own cubits {based on his arm span}. And if it troubles you why this measurement was not written {tani} together with other laws which the Rabbis stated are based upon the individual, this is because they did not regard this ruling as definite, for their is the person with stumped limbs, in which case his four arm-spans are not equal to tachtav, and we need to give him four cubits of the standard type of cubit.

{Eruvin 45a}
Mishna:
If there were two {people}, and a part of this one's cubits was within this one's cubits, they may bring and eat in the middle,
{Eruvin 45b}
provided that this one does not carry out from his into that of his fellow.
If there were three, and the middle one is enclosed between them, he is permitted with them and they are permitted with him, and the two outer ones are prohibited one with the other. Rabbi Shimon says: To what can this be likened? To three courtyards open to one another and open to the public domain; if the two of them made an eruv with the middle one - it is permitted with them and they are permitted with it, and the two outer ones are prohibited one with the other.

{Eruvin 48b}
Rav Yehuda cited Rav: These were the words of Rabbi Shimon. But the Sages say that the one domain may be utilized by the two domains, but the two domains may not be utilized by the one domain.
That is to say, the middle one may be utilized by the outer ones, but the outer one may not be utilized by the {residents of the} middle one.

{Eruvin 49a}
And Shmuel said: According to the Sages, all three are forbidden {to each other}.

Rav Chama bar Guria cited Rav: The halacha is like Rabbi Shimon.

{Eruvin 49b}
Mishna:
If a man was on a journey and darkness overtook him, and he knew of a tree or a fence, and he said, "My Shabbat station is under it" - he said nothing. "My Shabbat station is at its root" - he may walk from the place of his feet to its root 2,000 cubits and from its root to his house 2,000 cubits. Thus he can walk after nightfall 4,000 cubits.

If a person does not know {of a tree or a fence}, or if a person is not versed in the law, and he said, "My Shabbat station is in my place" - his place acquired for him 2,000 cubits in every direction.

"Round ones," says Rabbi Hanina ben Antignos. {That is, a circle with a radius of 2000 cubits.}
But the Sages say: Square ones, as a square board, so that he has the benefit of the corners.