Reference for Eruvin 178:12

אמר אביי בנה עלייה על גבי ביתו ועשה לפניה דקה ארבע הותר בכל הגגין כולן

'But did you not speak to us of dwellers? ' - 'If I spoke to you of dwellers I must have said this: They learned this<span class="x" onmousemove="('comment',' That the movement of objects is forbidden on the smaller roof.');">²¹</span> only where there was a partition that was suitable for a dwelling-place both on the one as well as on the other,<span class="x" onmousemove="('comment',' So that both groups evidently intended to use their respective roofs as dwelling-places.');">²⁹</span> since the use of the bigger roof is rendered permissible by the railings<span class="x" onmousemove="('comment',' Cf. supra p. 622, n. 19 mut. mut.');">³⁰</span>

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