Proof that private attacks are the “worst” attack in longest-chain blockchains

[jsoares]

It has been conjectured by David Tse and his co-authors that private attacks - i.e. attacks where the adversary creates a private chain, without contributing to the honest chain, in an attempt to outpace the honest chain - were the worst attack in longest-chain blockchains in the sense that the probability of success of any other attack is exponentially decreasing with the same exponent as private attacks.

Why is it important to Filecoin?

This is relevant to Filecoin as switching to a longest-chain protocol has been suggested as a way to remedy problems found in blockDAG blockchains (e.g. balance attacks).