Function propagate_core 

pub fn propagate_core<'scope, N, L, Tr, F, R>(
    edges: Arranged<'scope, Tr>,
    nodes: VecCollection<'scope, Tr::Time, (N, L), R>,
    logic: F,
) -> VecCollection<'scope, Tr::Time, (N, L), R>
where
    N: ExchangeData + Hash,
    R: ExchangeData + Abelian + Multiply<R, Output = R> + From<i8>,
    L: ExchangeData,
    Tr: TraceReader<Batch: Navigable, Time: Hash> + Clone + 'static,
    for<'a> BatchCursor<Tr>: Cursor<Key<'a> = &'a N, Val<'a> = &'a N, Time = Tr::Time, Diff = R>,
    F: Fn(&L) -> u64 + Clone + 'static,

Propagates labels forward, retaining the minimum label.

This variant takes a pre-arranged edge collection, to facilitate re-use, and allows a method logic to specify the rounds in which we introduce various labels. The output of `logic should be a number in the interval [0,64],