Reference for Eruvin 38:21

א"ל תניתוה ר' שמעון בן אלעזר אומר היתה שם אבן מרובעת רואין כל שאילו תחלק ויש בה אמה לכאן ואמה לכאן נידון משום דיומד ואם לאו אינו נידון משום דיומד

is subject to the law of a partition, and gaps in it [must not be wider] than ten cubits,<span class="x" onmousemove="('comment',' Lit., 'within (the limit of) ten'.');">⁴²</span> but those<span class="x" onmousemove="('comment',' The boards in a well enclosure.');">⁴³</span> are subject to the law of strips of wood and gaps of thirteen and a third cubits between then, [are allowed].<span class="x" onmousemove="('comment',' As such a partition is obviously much inferior than the others, only a limited area of two beth se'ah was allowed.');">⁴⁴</span>

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