in witness whereof
Formal legal expression used at the end of a document to introduce signatures or seals, confirming the authenticity of the preceding content.
In witness whereof, two copies of this document have been prepared, and after both parties have signed and sealed, each shall retain one copy.
A set legal phrase composed of 右 (the aforementioned), 証拠 (evidence/proof), and として (as). The exact historical derivation is uncertain, but it is conventionally used in Japanese legal documents.