Talmud zu Tahorot 7:4
אֵשֶׁת חָבֵר שֶׁהִנִּיחָה לְאֵשֶׁת עַם הָאָרֶץ טוֹחֶנֶת בְּתוֹךְ בֵּיתָהּ, פָּסְקָה הָרֵחַיִם, הַבַּיִת טָמֵא. לֹא פָסְקָה הָרֵחַיִם, אֵין טָמֵא אֶלָּא עַד מְקוֹם שֶׁהִיא יְכוֹלָה לִפְשֹׁט אֶת יָדָהּ וְלִגָּע. הָיוּ שְׁתַּיִם, בֵּין כָּךְ וּבֵין כָּךְ, הַבַּיִת טָמֵא, שֶׁאַחַת טוֹחֶנֶת וְאַחַת מְשַׁמֶּשֶׁת, דִּבְרֵי רַבִּי מֵאִיר. וַחֲכָמִים אוֹמְרִים, אֵין טָמֵא אֶלָּא עַד מְקוֹם שֶׁהֵן יְכוֹלִין לִפְשֹׁט אֶת יָדָן וְלִגָּע:
Die Frau eines Chavers [eine, die akribisch darauf achtet , alle seine Lebensmittel rein zu halten], die die Frau eines Am ha'aretz in ihrem Haus [dh das Haus der Frau des Chavers ] mahlen ließ , wenn das Mahlen aufhörte, das Haus ist unrein. Wenn das Fräsen nicht aufhörte, sind die Dinge nur so weit unrein, wo sie ihre Hand ausstrecken und berühren konnte. Wenn es zwei von ihnen gäbe [dh zwei Frauen von Amei Ha'aretz ], ist das Haus trotzdem unrein, weil eine Frau mahlen könnte, während die andere herumläuft und [andere Gefäße im Haus] berührt, so Rabbi Meir. Und die Weisen sagen: [selbst wenn es zwei von ihnen gibt] Dinge sind nur so weit unrein, wo sie ihre Hände ausstrecken und berühren könnten.
Jerusalem Talmud Avodah Zarah
Since the wine in the store is for sale, it is stored in open amphoras. The wine would become forbidden for usufruct if touched by the Gentile. In our Mishnah it seems that R. Meïr assumes that the Gentile will not touch the open amphoras. But in Mishnah Tahorot7:4 he holds that if a woman keeping all rules of ritual purity invites one careless in these matters to help her in her home all vessels in the home become impure since one must assume that the helper is impure and touches everything in sight.” Rebbi Ḥama in the name of Rebbi Yose bar Ḥanina: If a courtyard is subdivided by a low wall92The explanation is Rashi’s (70b, Bava batra 2b). The etymology is unknown; the word certainly is different from פְּסֵיפָס ψῆφος “pebble”., for purities it is impure, in matters of libation wine it is pure93A courtyard (in the back of houses or walled in, not directly open to the street) has been divided by a low wall as a sign that each party has only the use of its own part. Even though it is easy to step over the partition, the fact that it is raised is enough to create the presumption that the parties will abide by the rules and not trespass. If the dwellers in one part are scrupulous in observing the rules of purity while the others are not (or are Gentiles), the vessels standing in the courtyard of the observant party remain pure. Similarly, if one party is Jewish and the other Gentile, wine amphoras stored in the the Jewish part remain permitted since the presumption is that the Gentile will not enter the Jewish part., since Rebbi Meïr is restrictive for purities but lenient for libation wine; also the rabbis are restrictive for purities but lenient for libation wine94While a store catering to customers observant in matters of purity certainly cannot have a Gentile employee, a grocery store for the general public can have such an employee. In the Babli, 70b, this is reported as the opinion of Rav, opposed by R. Joḥanan..