"The proof-of-work involves scanning for a value that when hashed, such as with SHA-256, the hash begins with a number of zero bits. The average work required is exponential in the number of zero bits required and can be verified by executing a single hash."
Key Elements:
Computational search for specific hash patterns
Exponential difficulty scaling Easy verification but hard computation
What Bitcoin Actually Says About Proof-of-Work
From Section 4: Proof-of-Work
"The proof-of-work involves scanning for a value that when hashed, such as with SHA-256, the hash begins with a number of zero bits. The average work required is exponential in the number of zero bits required and can be verified by executing a single hash."
Key Elements:
Computational search for specific hash patterns
Exponential difficulty scaling
Easy verification but hard computation
Economic cost through electricity consumption
λ is to pure as POW is to action.