Reference for Eruvin 153:9
אמר רב שיזבי אמר רב נחמן חריץ שבין שתי חצירות צידו אחד עמוק עשרה וצידו אחד שוה לארץ נותנין אותו לזה ששוה לארץ משום דהוה ליה לזה תשמישו בנחת ולזה תשמישו בקשה וכו'
because the use of it is convenient to the latter but inconvenient to the former, and any place the use of which is convenient to one and inconvenient to another, is to be assigned to the one to whom its use is convenient. R'Shezbi laid down in the name of R'Nahman: A trench between two courtyards, whose one side was ten handbreadths deep<span class="x" onmousemove="('comment',' I.e., the level of the floor of the courtyard adjacent to it was ten handbreadths higher than the level of the bed of the trench.');"><sup>23</sup></span> and whose other side was on a level with<span class="x" onmousemove="('comment',' Sc. 'not lower than ten handbreadths from',');"><sup>24</sup></span>