[tromp]

> The term “proof of work” is apt. The work is the proof. Finding a valid hash demonstrates that you did the computational work to find it.

This whole article equates Proof of Work with hashing.

But the term Proof of Work is more general than the particular instance used in Bitcoin (Hashcash).

Other forms of Proof of Work require finding a solution to a puzzle after fixing the header and nonce. For example, Cuckoo Cycle requires finding a 42-cycle in a huge bipartite graph.