I was wondering how a new node can bootstrap and be sure it has a valid set of balances, when all the other nodes have discarded the transaction history. Just having proof of work doesn't tell you that all the transactions in those blocks are valid to you, just that they were valid to whoever mined them. But it sounds like that issue is addressed fairly well at the bottom of the "Proof Chain" section.

School is calling, don't get ur teacher panic & lock ur earfucked head in a headlock.