Hal Finney's server-backed system that transformed Hashcash proofs into transferable tokens without redoing the work.
Reusable Proofs of Work is best understood as part of a system rather than as an isolated definition. Its related coordinates show the mechanisms, incentives and historical records that give the term practical meaning.
Reusable Proofs of Work belongs to the documented history and social layer around Bitcoin. Primary records can establish what was published, built or decided; motives, influence and later interpretation should remain separate from those verifiable facts.
Understanding Reusable Proofs of Work helps distinguish a verifiable Bitcoin mechanism or historical record from slogans, products and market narratives.
For the clearest picture, read this entry together with Hal Finney, Hashcash, Proof of Work. The reverse links also lead from Hal Finney.
Linked to related atlas coordinates
Grounded in a source record
Explains function and trade-offs
Part of the open Bitcoin knowledge graph