עירובין א׳Eruvin 1

Mishnah 1א׳

מָבוֹי שֶׁהוּא גָבוֹהַּ לְמַעְלָה מֵעֶשְׂרִים אַמָּה, יְמַעֵט. רַבִּי יְהוּדָה אוֹמֵר, אֵינוֹ צָרִיךְ. וְהָרָחָב מֵעֶשֶׂר אַמּוֹת, יְמַעֵט. וְאִם יֶשׁ לוֹ צוּרַת הַפֶּתַח, אַף עַל פִּי שֶׁהוּא רָחָב מֵעֶשֶׂר אַמּוֹת, אֵין צָרִיךְ לְמַעֵט:

If a mavoy [an alleyway onto which courtyards open] - that [has an entrance with an opening that] is higher than twenty amot [a specific unit of length], one must lower [it in order to separate the mavoy from the public domain]. Rabbi Yehuda says it is not necessary. And if it is wider than ten amot, one must narrow [it in order to separate the mavoy from the public domain]. If there is a tsurat hapetach [two uprights and a crossbar, however slight, halachically effecting a doorway], even though [the entrance] is wider than ten amot, it is not necessary to narrow it.

Mishnah 2ב׳

הֶכְשֵׁר מָבוֹי, בֵּית שַׁמַּאי אוֹמְרִים, לֶחִי וְקוֹרָה, וּבֵית הִלֵּל אוֹמְרִים, לֶחִי אוֹ קוֹרָה. רַבִּי אֱלִיעֶזֶר אוֹמֵר, לְחָיַיִן. מִשּׁוּם רַבִּי יִשְׁמָעֵאל אָמַר תַּלְמִיד אֶחָד לִפְנֵי רַבִּי עֲקִיבָא, לֹא נֶחְלְקוּ בֵּית שַׁמַּאי וּבֵית הִלֵּל עַל מָבוֹי שֶׁהוּא פָחוֹת מֵאַרְבַּע אַמּוֹת, שֶׁהוּא אוֹ בְלֶחִי אוֹ בְקוֹרָה. עַל מַה נֶּחְלְקוּ, עַל רָחָב מֵאַרְבַּע אַמּוֹת וְעַד עֶשֶׂר, שֶׁבֵּית שַׁמַּאי אוֹמְרִים, לֶחִי וְקוֹרָה, וּבֵית הִלֵּל אוֹמְרִים, אוֹ לֶחִי אוֹ קוֹרָה. אָמַר רַבִּי עֲקִיבָא, עַל זֶה וְעַל זֶה נֶחֱלָקוּ:

The required preparation of a mavoy [to consider its fourth side as separated from the public domain]: Beit Shammai says, "A lechi [A vertical strip at the side of an entrance to a mavoy which permits carrying on Shabbat in the mavoy] and a beam [on top of the entrance]." Beit Hillel says, "A lechi or a beam." Rabbi Eliezer says, "Two lechi." In the name of Rabbi Yishmael, said one student in front of Rabbi Akiva, "Beit Shammai and Beit Hillel did not disagree about [an entrance of] a mavoy that is narrower than four amot, that it is [adequately separated] with either a lechi or a beam. About what did they disagree? About [an entrance of a mavoy] that is from four to ten amot; Beit Shammai says, '[It needs] a lechi and a beam,' but Beit Hillel says, 'Either a lechi or a beam.'" Rabbi Akiva says, "They disagreed about this and that."