Bava Batra 163 - Prevention of Document Forgeries
Rav said that a certified document with both its text and the signatures of its witnesses written on erased parchment is valid, if it can be discerned that it was erased only once. But maybe he erased the document and the signatures, wrote a new document, forged the signatures, and re-used the certification? Rav answers that such a document is certified not from the certification written in it but from the signatures; thus, the forger gains nothing.
Art: Drawing Board Pipe Onions And Sealing Wax by Van Gogh
