פירוש על שבועות 6:1

21. If a document is on paper and its witnesses are on erasure, the document is disqualified because the party might erase the document and forge it, resulting in the text and witnesses both on erasure. If the witnesses write, “we the witnesses signed on erasure while the document was on paper,” the document is valid, so long as they wrote it between the signatures of the first and second witnesses. If, however, they wrote it before or after their signatures, the declaration would be of no effect.