Reference for Bava Batra 127:3

ואי ס"ד בסתמא לא קני למה לי על מנת אהני ליה על מנת דאי נפיל הדר בני לה:

— What he gains by the stipulation is the right to rebuild it if it falls in.<span class="x" onmousemove="('comment',' This right not being conveyed by the bare transfer, which relates to 'this' layer only. Hence if he desires to transfer the roof completely, he must insert the words 'depth and height'. ');">⁵</span> <b><i>MISHNAH</i></b>. [THE VENDOR OF A HOUSE DOES NOT SELL THEREWITH] A WELL OR A CISTERN,<span class="x" onmousemove="('comment',' The difference between these terms is explained in the Gemara. ');">⁶</span>

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