Reference for Bava Batra 327:1

ואם תאמר מוחק וחוזר ומוחק אינו דומה נמחק פעם אחת לנמחק שתי פעמים

If, however, it is objected<span class="x" onmousemove="('comment',' Lit., 'thou wilt say'. ');">¹</span> [that, since the writing on the document had been] erased [once, it might] be erased again,<span class="x" onmousemove="('comment',' And, consequently, while leaving the signatures on the first erasure, the text above them could be erased again. and on this second erasure a forged text might be substituted for the original! ');">²</span> [it may be replied that anything which] has been erased once is not like [that which] has been erased twice.<span class="x" onmousemove="('comment',' The forgery would be discovered by comparing the signatures which appear on a first erasure with the text appearing on a repeated erasure. ');">³</span>

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