Eruvin 94B

וכגון שנפרצה בקרן זוית. דפיתחא בקרן זוית לא עבדי אינשי.

and with a case where the courtyard was breached in a corner, so that it is breached on two sides. Although the opening is no more than 10 cubits wide, it cannot be considered an entrance, as people do not build an entrance in a corner. It is therefore clear that this is a breach that negates the partition.

וכן בית שנפרץ משתי רוחותיו. מאי שנא מרוח אחת, דאמרינן: פי תקרה יורד וסותם. משתי רוחות נמי לימא: פי תקרה יורד וסותם!

We learned in the Mishnah: And likewise, with regard to a house that was breached on Shabbat from two of its sides into a public domain, the residents are permitted to carry in the house on that Shabbat, but not a future Shabbat. The Talmud asks: In what way is a breach on one side different? The difference is due to the fact that we say: The edge of the roof descends and seals the house, as if there were a full-fledged partition there. So too, when it is breached on two sides, let us say: The edge of the roof descends and seals.

אמרי דבי רב משמיה דרב: כגון שנפרץ בקרן זוית וקירויו באלכסון, דליכא למימר פי תקרה יורד וסותם.

The Talmud answers: The rabbis of the school of Rav said in the name of Rav: The Mishnah is referring to a case where the house was breached in a corner, and its roofing was inclined, as in that case, one cannot say: The edge of the roof descends and seals, as the edge of an inclined roof does not appear to be the beginning of a partition.

ושמואל אמר: אפילו ביתר מעשר. אי הכי, מרוח אחת נמי!

And Shmuel said: The Mishnah is referring to a breach that is even wider than 10 cubits. The Talmud asks: If so, why did the Mishnah cite a case where it is breached from two sides? It should be prohibited to carry there even if it were breached from one side.