Reference for Bava Batra 327:4

מיתיבי הוא על הנייר ועדיו על המחק כשר וניחוש דלמא מחיק ליה וכתיב מאי דבעי והוי ליה הוא ועדיו על המחק

a repeated erasure?<span class="x" onmousemove="('comment',' Lit., 'erased twice'; and since both text and signatures would thus appear on the same kind of erasure, the court would not be able to detect the forgery. ');">¹⁰</span> — Abaye replied: Rab is of the opinion [that] Witnesses [must] not sign on an erasure unless the erasure was made<span class="x" onmousemove="('comment',' Lit., 'it was erased'. ');">¹¹</span> in their presence.<span class="x" onmousemove="('comment',' They would, consequently, be able to satisfy themselves that the upper and lower sections of the erasure were exactly alike. ');">¹²</span>

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