Rif Succah 6b {Succah 11b continues; 12a-b}

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6b

{Succah 11b continues}
And so too in terms of tzitzit, if he suspended them and tied them, and afterwards separated {by snipping} their strings, they are invalid. And we do not say that their cutting is their creation.

{Succah 12a}
"This is the general rule: that which is not susceptible to ritual impurity...":
From where do we know this?
Rabbi Yochanan said: The verse states {Devarim 16:13}:

יג חַג הַסֻּכֹּת תַּעֲשֶׂה לְךָ, שִׁבְעַת יָמִים: בְּאָסְפְּךָ--מִגָּרְנְךָ, וּמִיִּקְבֶךָ.

13 Thou shalt keep the feast of tabernacles seven days, after that thou hast gathered in from thy threshing-floor and from thy winepress.

With the byproducts of your threshing-floor and your winepress Scriptures is speaking.

Rav Chisda said: From here: {Nechemia 8:15}:

טו וַאֲשֶׁר יַשְׁמִיעוּ, וְיַעֲבִירוּ קוֹל בְּכָל-עָרֵיהֶם וּבִירוּשָׁלִַם לֵאמֹר--צְאוּ הָהָר וְהָבִיאוּ עֲלֵי-זַיִת וַעֲלֵי-עֵץ שֶׁמֶן, וַעֲלֵי הֲדַס וַעֲלֵי תְמָרִים וַעֲלֵי עֵץ עָבֹת: לַעֲשֹׂת סֻכֹּת, כַּכָּתוּב. {פ}

15 and that they should publish and proclaim in all their cities, and in Jerusalem, saying: 'Go forth unto the mount, and fetch olive branches, and branches of wild olive, and myrtle branches, and palm branches, and branches of thick trees, to make booths, as it is written.' {P}

hadas = "branches of thick trees?"
Rav Chisda said: A foolish myrtle {hadas shoteh} for succah and branches of thick trees {= regular hadas} for lulav.

Mishna:
Bundles of straw, bundles of wood, and bundles of twigs must not be used to cover the Succah; all of these are become valid, however, if the bundles are loosed. As side-walls, however, all of these may be used.

Gemara:
Rabbi Chiyya bar Abba cited Rabbi Yochanan: Why did they say that bundles of straw, bundles of wood, and bundles of twigs must not be used to cover the Succah? Not because they are forbidden as schach but rather there are times that a man comes from the field with his bundle on his shoulder, and he lifts it up and places it on top of a succah to dry it out, and changes his mind upon it that it should be schach. And the Torah states {Devarim 16:13} תַּעֲשֶׂה and not from that which is made of its own accord.

{Succah 12b}
Rav Yehuda said: If he used arrow shafts for schach: the "males" are valid {shafts of arrows -- see computer terminology for parallels} but the "females" are invalid {hollow-tipped shafts into which the arrowheads are inserted}, for they have a bet kibbul {a hollow}, and even though it is made specifically to be filled it is still called a bet kibbul.

Rabba bar Rav Huna cited Rav: If he covered it {=the succah} with combed flax {anitzei pishtan} it is invalid; with stalks of flax {hutznei pishtan} it is valid.

To explain hutznei: