Bava Batra 61B

לא צריכא, דאף על גב דמצר ליה מצרי אבראי –

No, this ruling is necessary to teach that the room behind the house is excluded from the sale of the house even if the seller delineated the boundaries of the house for the buyer in the bill of sale by listing places outside the room, e.g., noting the houses that border the property being sold. Even though this might suggest that the room is included in the sale, the Mishnah teaches that it is not.

כדרב נחמן, דאמר רב נחמן אמר רבה בר אבוה: המוכר בית לחבירו בבירה גדולה, אף על פי שמצר לו מצרים החיצונים ⁠– מצרים הרחיב לו.

This is in accordance with the opinion of Rav Naḥman, as Rav Naḥman says that Rabba bar Avuh says: With regard to one who sells a residence to another in a large building [bira] containing several residences, even if he delineates for him the external boundaries of the large building, he did not sell him the entire building, but rather he enlarged upon the boundaries for him. That is, the seller did not mean to delineate the precise borders of what he was selling; rather, he delineated the boundaries in a broad manner, giving the general location of the specific residence subject to the transaction.

היכי דמי? אילימא דקרו ליה לבית ״בית״ ולבירה ״בירה״, פשיטא ⁠– בית זבין ליה, בירה לא זבין ליה! אלא דלבירה נמי קרו לה ״בית״? כוליה זבין ליה!

With regard to Rav Naḥman’s statement, the Talmud inquires: What are the circumstances of the case? If we say that this is referring to a place where they call a residence a residence, and a building a building, and they always differentiate between the two terms, it is obvious that he did not intend to sell him the entire building but merely enlarged upon the boundaries for him, as he sold him a residence and did not sell him a large building. Rather, explain that this is referring to a place where they also call a building a residence. But in that case, why not say that the seller sold him the entire building, since he delineated the external boundaries of the large building?