Looks that arkworks does not have the implementation of proof of work (even the simplest one). We can probably add one here (use the one similar to libiop? )

We can use existing CRH trait to make it generic. Also, we will need to write the constraints. (For now all CRH has its constraints written, so we just need to wrap it.)

"one line algo"

For a message M and difficulty k, the prover will bruteforce a nonce N such that the last k bits of the output of H(M || N) are zero.