עירובין ז׳Eruvin 7

Mishnah 1א׳

חַלּוֹן שֶׁבֵּין שְׁתֵּי חֲצֵרוֹת, אַרְבָּעָה עַל אַרְבָּעָה, בְּתוֹךְ עֲשָׂרָה, מְעָרְבִין שְׁנַיִם, וְאִם רָצוּ, מְעָרְבִין אֶחָד. פָּחוֹת מֵאַרְבָּעָה עַל אַרְבָּעָה, אוֹ לְמַעְלָה מֵעֲשָׂרָה, מְעָרְבִין שְׁנַיִם וְאֵין מְעָרְבִין אֶחָד:

An opening (in a wall) between two courtyards, four by four (handbreadths) in the midst of ten (tefachim) from the ground [i.e., if part of it, even a very small part, is ten tefachim from the ground] — two eruvin are made, [each (courtyard) for itself, and each forbids (carrying from one to) the other.] And if they wish, they make one eruv, [these (the men of one courtyard) placing their eruv in the other and being one with them (the men of the other courtyard)]. Less than four by four or higher than ten, two eruvin are made and one is not made. [Less than four by four is not (considered) an opening and is not fit for passing from one to the other. And if it is above ten, too, it does not lend itself to use. Therefore, one eruv is not made. This, only in an unroofed courtyard; but in a roofed house, even higher than ten, one eruv is made, it being customary to place benches and boxes around the house, so that it lends itself to use.]

Mishnah 2ב׳

כֹּתֶל שֶׁבֵּין שְׁתֵּי חֲצֵרוֹת גָּבוֹהַּ עֲשָׂרָה וְרָחָב אַרְבָּעָה, מְעָרְבִין שְׁנַיִם וְאֵין מְעָרְבִין אֶחָד. הָיוּ בְרֹאשׁוֹ פֵרוֹת, אֵלּוּ עוֹלִין מִכָּאן וְאוֹכְלִין, וְאֵלּוּ עוֹלִין מִכָּאן וְאוֹכְלִין, וּבִלְבַד שֶׁלֹּא יוֹרִידוּ לְמַטָּה. נִפְרְצָה הַכֹּתֶל עַד עֶשֶׂר אַמּוֹת, מְעָרְבִין שְׁנַיִם, וְאִם רָצוּ מְעָרְבִין אֶחָד, מִפְּנֵי שֶׁהוּא כְפֶתַח. יוֹתֵר מִכָּאן, מְעָרְבִין אֶחָד וְאֵין מְעָרְבִין שְׁנָיִם:

A wall between two courtyards ten (tefachim) high and four wide — two eruvin are made and not one. ["four" is taught, not because this amount is required for "closing off" (one courtyard from another), for a partition of any breadth constitutes "closing off," but (it is taught) by reason of what follows, viz.:] If there were fruits on top of it, these go up from here (i.e., from their courtyard) and eat, and those go up from there and eat, so long as they do not take it down [to the house-dwellers; but to the courtyard it is permitted. For it (a four-handbreadth wide partition) is considered a domain in itself. It is in this regard that four handbreadths are required, less than that constituting a makum p'tur ("a place of exemption) and both being permitted to take it down.] If the wall were breached, up to ten cubits, they make two eruvin; and if they wish, they make one, for it is like an opening. (If it is) more than that, they make one eruv and not two. [(For if it is more) it is a breach, and it is all considered one courtyard. And if each made an eruv for itself, it is as if they (the men of one courtyard) are dividing their eruvin, and they forbid each other.]