let mut unknown_children = Vec::new();

            debug!("-> {:?}", v);

            if v.flag().contains(EdgeFlags::PARENT) {
                // Unwrap ok, since `v` is in the channel.
                let intro = txn.get_external(&v.dest().change)?.unwrap().into();
                if !known(&intro) {
                    debug!("unknown: {:?}", v);

            // Unwrap ok, since `v` is in the channel.
            let intro = txn.get_external(&v.dest().change)?.unwrap().into();
            if !known(&intro) {
                debug!("unknown: {:?}", v);
                if v.flag().contains(EdgeFlags::PARENT) {

                } else {
                    unknown_children.push((dest_vertex, *v));

            } else {
                debug!("known {:?}", v);

        debug!("unknown parents {:?}", unknown_parents);
        debug!("unknown children {:?}", unknown_children);

        zombify_down(
            txn,
            channel,
            ws,
            change_id,
            inode,
            n.flag,
            &unknown_children,
        )?;

fn zombify_down<T: GraphMutTxnT>(
    txn: &mut T,
    channel: &mut T::Graph,
    ws: &mut crate::missing_context::Workspace,
    change_id: ChangeId,
    inode: Position<Option<Hash>>,
    flag: EdgeFlags,
    unknown: &[(Vertex<ChangeId>, SerializedEdge)],
) -> Result<(), MissingError<T::GraphError>> {
    for &(dest_vertex, edge) in unknown.iter() {
        let p = *txn.find_block(channel, edge.dest())?;
        ws.unknown_parents
            .push((dest_vertex, p, inode, edge.flag()));
        let fold = flag & EdgeFlags::FOLDER;
        debug!("zombify p {:?}, dest_vertex {:?}", p, dest_vertex);
        let mut u = dest_vertex;
        let mut v = edge.dest();
        while let Ok(&v_) = txn.find_block(channel, v) {
            if v_ != u {
                debug!("u = {:?}, v = {:?}", u, v);
                put_graph_with_rev(
                    txn,
                    channel,
                    EdgeFlags::DELETED | EdgeFlags::BLOCK | fold,
                    u,
                    v_,
                    change_id,
                )?;
                u = v_;
                v = v_.end_pos()
            } else {
                break;
            }
        }
    }
    Ok(())
}