Function fork_check 

pub fn fork_check(
    seed: &str,
    statement: &SignedStatement,
    home_node: &str,
    current: &str,
    chain: &SnapshotChain,
) -> Check

The fork rule applied to one seed’s statement (D80), with nothing fetched: the statement, the node id and current attestation the home showed this reader, and the chain read from the home’s own log.

Pure so the one judgement that can call a home a liar is testable against a forged statement without a node that would forge one.