Function sequence 

pub fn sequence(
    runtime: &Runtime,
    state: &Value,
    base: Seq,
    seen: &mut Seen,
    batch: Vec<Proposal<'_>>,
    meter: &dyn Meter,
) -> Committed

Decide a batch: what becomes an event, what each proposer is told, and the state that follows.

Pure with respect to the machine — it reads no clock and touches no store — but not with respect to seen, which is the application’s idempotency memory and moves as commands are accepted.