Reference for Eruvin 121:9

אמר רב יוסף אמר רמי בר אבא אמר רב הונא עיר שיושבת על שפת הנחל אם יש לפניה דקה ארבעה מודדים לה משפת הנחל ואם לאו אין מודדין לה אלא מפתח ביתו

in height in front of it, its Sabbath limit is measured from the edge of the ravine,<span class="x" onmousemove="('comment',' Which is regarded as the boundary of the town.');">²⁵</span> otherwise<span class="x" onmousemove="('comment',' Lit., 'and if not', i.e., if no such partition was provided.');">²⁶</span> measuring<span class="x" onmousemove="('comment',' Of the Sabbath limit of the town.');">²⁷</span> must begin from the door of every inhabitant's house.<span class="x" onmousemove="('comment',' All the town, in the absence of the partition, being regarded, for the reason to be given presently, as an occasional and irregular settlement which, in respect of Sabbath limits, cannot be treated as one unit of four cubits. Every house must be considered as a separate unit and the Sabbath limit of its tenants begins from that house.');">²⁸</span>

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