Rif Eruvin 11b {Eruvin 42b continues ... 43b}

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11b

{Eruvin 42b continues}
What is the reason?
Rabba said: Since he established his place of Shabbat rest within the space of the partitions {of the boat} while it was yet day {Friday}.
Rabbi Zera said: Since his boat transports him from the beginning of his four cubits and places him at the end of his four cubits.
What is the difference between them? This is the difference between them: Where the walls of the boat were opened. Alternatively, where he jumps from one boat to another boat. According to Rabba, who said it is because he established his place of Shabbat rest within the space of the partitions, here it is forbidden, for he did not establish his place of Shabbat rest within the space of the partitions. According to Rabbi Zera, it is permitted, since the boat brings him from the beginning of four cubits and deposits him at the end of four cubits.

Why did Rabbi Zera not say like Rabba?
{Eruvin 43a}
The walls {of the boat} are constructed to keep the water out.
And why did Rabba not say like Rabbi Zera?
Where it travelled, all would agree that it is permitted. Where do they argue? When it is standing still. And we can derive this also from the language of our Mishna like Rabba, for it states a boat, similar to {the two other examples} a pen and a fold. Just as a pen and a fold are fixed in place, so too the boat when it is fixed in place.

And the {post-Talmudic} sages rule like Shmuel - even though in general, the halacha is like Rav as regards prohibitions, here the halacha is like Shmuel, for there is a brayta like him. For they learnt {in a brayta}: Chanania says: All that day they sat and discussed the halachic matters. The next day my father's brother was machria {=decided. The word here and in other situations really means "compromised," and it is the interpretation of "decided" that causes the Rif difficulty here} amongst them and said: The words of Rabban Gamliel appear {correct} regarding a boat, and the words of Rabbi Akiva regarding a pen and a fold.

And we {=Rif} do not hold like this, for we only learn from this Tanna that Rabban Gamliel and Rabbi Akiva argue, but a support to one of them we do not find, for we have established for ourselves that we do not learn halacha from Mishna nor from Talmud {here, Talmud=brayta; alternatively, emend to "but rather from talmud" by changing ולא into אלא. See Ran - of course one would pasken from gemara - Ravina and Rav Ashi generation}.
And if we say "but he was machria!" and we have established that anytime two argue and one {= a third party} is machria, we said on this is perek Kira {Shabbat 40a} that perhaps this saying {=rule for deciding halacha} is only regarding Mishna but not regarding brayta. And furthermore, the brother of the father of Chanania was Rabbi Yehoshua, and how can he simultaneously be a disputant and a machria? Therefore, we return to the {trusty} rule that the halacha is like Rav regarding prohibitions and like Shmuel in dinim. And further, this that we say later on that regarding Nechemia the son of Rav Huna bar Chanilai {Eruvin 44a}: "And if it enters your mind that we are dealing with a case in which it was lined with people {thus forming a partition}, Rav said that the halacha is like Rabban Gamliel by a pen, a fold and a boat," which makes it clear that the halacha is like Rav.

{Eruvin 41b}
Mishna:
Once they did not enter the harbor until nightfall.
They said to Rabban Gamliel: May we disembark?
He said to them: You may, for I had already looked, and we were within the bounds before nightfall.

{Eruvin 43b}
Gemara:
They learnt {in a brayta}: Rabban Gamliel had a tube {=telescope} through which he would look 2000 cubits on land and, parallel to that, on the sea. And one who wishes to know the depth of a velley should bring a telescope and look on {regular land, straightforward} and he will know the depth of the valley {by seeing how far he can see with the telescope}.

Nechemia the son of Rav Huna bar Chanilai was preoccupied with his learning and exited outside of the techum. Rav Chisda said to Rav Nachman: Nechemia your student