Reference for Eruvin 178:6

ואמרת לן עלה אמר רב יהודה אמר שמואל לא שנו אלא שיש דיורין על זה ודיורין על זה דהויא לה הא דקטן מחיצה נדרסת

to mean, 'that one must not move an object along two cubits on one roof and along another two cubits on an adjacent roof', so we might also explain this:<span class="x" onmousemove="('comment',' The Baraitha cited by the school of Samuel.');">¹¹</span> Two cubits on one roof and two cubits on the other.<span class="x" onmousemove="('comment',' Within the same roof, however, it is permitted to move an object within four cubits, but no further.');">¹³</span> R'Joseph<span class="x" onmousemove="('comment',' Who after a serious illness had lost his memory.');">¹⁴</span>

Jastrow