Reference for Gittin 66:11

ומדהא כרבן שמעון בן גמליאל הך כרבי

— Said R. Ashi: If the two are witnesses to the Get, then Rabban Simeon would also admit [that he can countermand separately].<span class="x" onmousemove="('comment',' Because no harm can possibly ensue, as one signature by itself is worthless. ');">¹¹</span>

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