Reference for Eruvin 167:16

הא דביני ביני אסור

hence both were required. Come and hear: If the tenants of a courtyard and the tenants of the upper storey forgot to prepare a joint 'erub,<span class="x" onmousemove="('comment',' But each group prepared one for itself.');">³³</span> the former may use<span class="x" onmousemove="('comment',' Along the wall.');">³⁴</span>

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