Function strongly_connected_at 

pub fn strongly_connected_at<'scope, T, N, R, F>(
    graph: VecCollection<'scope, T, (N, N), R>,
    logic: F,
) -> VecCollection<'scope, T, (N, N), R>
where
    T: Timestamp + Lattice + Hash,
    N: ExchangeData + Hash,
    R: ExchangeData + Abelian + Multiply<R, Output = R> + From<i8>,
    F: Fn(&N) -> u64 + Clone + 'static,

Returns the subset of edges in the same strongly connected component.

This variant introduces node labels in rounds indicated by logic, as in propagate_at: small labels can complete their propagation before larger labels are introduced, which can substantially reduce the total work performed.