This is a pretty bad name, as this doesn't store UTXOs.

Using proof and proofs doesn't help comprehend what this does.

I don't think you need emplace here. Just insert.

This whole thing is an order of magnitude more complex than it needs to.

Just use an array, and do something akin to

for (auto &p : proofs) {

if (proof.isbeterthan(p)) {
    swap(p, proof);
}

}

if p(roof != nullptr) removeProof(proof);

But the more I read this, the more I question the whole approach. The complexity is clearly not in proprotions to what this is doing - (effectivel a multimap with some prunning).

This isn't a map of utxo, this is a map from utxo to proofs. So it is a map of proofs, but considering this is in the proof pool, this isn't super informative.

Do we really want to keep more than 1? And if the size is 2, do w really want to crate all these sets? Just store two pointers in there, no?

shifted?