Rif Eruvin 25a {Eruvin 79a continues ... 79b; 49a}

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25a

{Eruvin 79a continues}
only if he laid the length of the board across the width of the ditch. But if he laid the length of the board across the length of the ditch, and even if the width of the board is any minute amount, they make one eruv, for he has reduced the {width of} the ditch from four handbreadths.

"And similarly, two balconies...":
Rava said: They only learned this where one was opposite the other, but if this one is not opposite the other, or one is higher than the other, no.
And they only said this {that vertical distance matters} for the case where there was between them three handbreadths {vertically}, but if there is not between them three, it is reckoned as a single crooked balcony and is permitted.

Mishna:
If a heap of straw between two courtyards is ten handbreadths high – they make two eruvs and they may not make one eruv. These feed from here and these feed from here.
If the straw was reduced to less than ten tefahs – they make one eruv and they may not make two eruvs.

Gemara:
"If a heap of straw between two courtyards...":
Rav Huna said: Provided no one puts staw into his basket and feeds {but rather the cattle must eat directly from the heap}. {Implying that} to place cattle there {such that they will eat} is permitted. But Rav Yehuda cited Rabbi Chanina: A man may place his animal by grass on Shabbat, but not by muktzeh on Shabbat. He only stands next to it {such that it does not stray} and it itself goes and eats.

{Eruvin 79b}
Mishna:
How do they participate {=make a shittuf} in the alleyway? He places there a cask and he says: "This belongs to all the people of the alleyway."
And he confers possession upon them through his adult son or daughter, through his Hebrew manservant and maidservant, and through his wife; but he does not {confer possession} through his son or his daughter that are minors, or by his Canaanite bondman or bondwoman, because their hand is as his hand.

Gemara:
Rav Yehuda said: The cask of the shittuf of the alleyway, he must lift it up {when making the acquisition} from the ground a handbreadth.
Rava said: These two things, the elders of Pumpedita said. One of them was this {=the aforementioned} and the other was: he who recites kiddush, if he tasted a cheekful, he has fulfilled {his obligation} and if not, he has not fulfilled.

{Eruvin 49a}
Rav Yehuda cited Shmuel: If someone divides his eruv, his eruv is no eruv. Like whom? Like Bet Shammai