pub fn new(iterator: I) -> Self {
            Self {
                iterator,
                updates: std::collections::HashSet::new(),
                reported_frontier: Antichain::from_elem(T::minimum()),
                progress_frontier: Antichain::from_elem(T::minimum()),
                messages_frontier: MutableAntichain::new(),
                progress_queue: Vec::new(),
            }
        }
Construct a new re-ordering, deduplicating iterator.
differential-dataflow/src/capture.rs