| 摘要 |
PROBLEM TO BE SOLVED: To provide a simple and low-cost method for proving the forming date of a document or the like. SOLUTION: The inner surfaces of left end pieces of three-folds of a sheet folded up to the three-folds with its one surface disposed at its inside are formed as recording surfaces. The inner surface of a central piece is coated with a carbon. The inner surface of the right end piece and the outer surface of the left end piece are coated with an adhesive which cannot be returned to its original when once adhered and released. In this case, the document is written on the recording surface. Then, the outer surface of the central piece is used for a mail as the front surface of the mail. Thus, the date is proved by copying the transfer seal shadow by the carbon of a postmark on the recording surface by pressing the postmark.
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