Reference for Tahorot 6:9

הַפָּרָן, רְשׁוּת הַיָּחִיד לַשַּׁבָּת וּרְשׁוּת הָרַבִּים לַטֻּמְאָה. וְכֵן הַצְּדָדִין. רַבִּי מֵאִיר אוֹמֵר, הַצְּדָדִין, רְשׁוּת הַיָּחִיד לְכָךְ וּלְכָךְ:

A forum is a private domain regarding Shabbat, but a public domain regarding impurity; and similarly the sides [of the forum are also a private domain regarding Shabbat and a public domain regarding impurity]. Rabbi Meir says: the sides are a private domain regarding both of them.

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