Reference for Eruvin 186:10
בעי רב הושעיא דיורין הבאין בשבת מהו שיאסרו
deals with a case, for instance, where the gap extended along a whole side of the lower courtyard.<span class="x" onmousemove="('comment',' Lit., 'where the lower one was broken in its fullness into the upper one', the width of the upper one not exceeding ten cubits, so that the tenants of the latter, in the absence of a joint 'erub, impose restrictions on the tenants of the former.');"><sup>27</sup></span> If so should not the tenants of the lower one be allowed to prepare a single 'erub [jointly]<span class="x" onmousemove="('comment',' With those of the upper one (cf. prev. n.) .');"><sup>28</sup></span> but not one for themselves alone<span class="x" onmousemove="('comment',' Lit., ' (one of) two'.');"><sup>29</sup></span>