Rif Succah 8a {Succah 15a continues}

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8a

{Succah 15a continues}
He must loosen them or remove one from between them {the two}. And Bet Shammai say: He must loosen them and remove one from between them.

Rabbi Meir says: He must remove one from between them and he need not loosen them.

Gemara:
The reason of Bet Hillel is that they must be made {as the verse states תעשה} and should not be made of their own accord. Therefore if he loosens them he makes an action and if he takes one from between them he makes an action.
And so is the halacha.

Mishna:
If one roofs his succah with iron spits, or with boards of a bedstead, if there is space between them just like them, it is valid.
If one should hollow out a space in a stack (of sheaves) to use it as a succah, it is not considered a succah.