> For the complete documentation index, see [llms.txt](https://chainx-2.gitbook.io/chainx/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://chainx-2.gitbook.io/chainx/proof-of-personhood-pop/building-blocks/deduplication.md).

# Deduplication

For a PoP to be useful, it needs to have a notion of uniqueness. If the PoP can be acquired multiple times and transferred to fraudulent actors or bots, it cannot be trusted and fails to serve its purpose. Therefore, a PoP mechanism needs to deduplicate between the users that are issued a proof of personhood credential. This is the hardest challenge for any PoP mechanism.