fn stash_updates_for_val(&mut self, source: &OrdValStorage<L>, index: usize) {
            let (lower, upper) = source.updates_for_value(index);
            for i in lower .. upper {
                // NB: Here is where we would need to look back if `lower == upper`.
                let time = source.times.index(i);
                let diff = source.diffs.index(i);
                use crate::lattice::Lattice;
                let mut new_time: <L::Target as Update>::Time = time.into_owned();
                new_time.advance_by(self.description.since().borrow());
                self.update_stash.push((new_time, diff.into_owned()));
            }
        }
Transfer updates for an indexed value in `source` into `self`, with compaction applied.
differential-dataflow/src/trace/implementations/ord_neu.rs