Reference for Eruvin 121:17
רב ספרא אמר עיר העשויה כקשת הואי
R'Dimi B'Hinena explained: The former<span class="x" onmousemove="('comment',' The people of Gader.');"><sup>53</sup></span> were the inhabitants of a large town while the latter were inhabitants of a small town.<span class="x" onmousemove="('comment',' The Sabbath limit of Gader terminated at the far end of Hamethan (the smaller town) while the Sabbath limit of Hamethan terminated in the middle of the large town of Gader. As all Hamethan lay within the Sabbath limit of Gader the people of the latter town were permitted to traverse its whole area (as if all the town were no bigger than four cubits) and distances completing the permitted two thousand cubits beyond it. As part of Gader, on the other hand, was without the Sabbath limit of Hamethan the people of the latter town could walk only to the end of their Sabbath limit.');"><sup>54</sup></span> Thus<span class="x" onmousemove="('comment',' Specifying the authorship of each of the two last mentioned explanations.');"><sup>55</sup></span> taught R'Kahana.