fn iter_graph(

    fn graph_cursor(

    fn iter_graph<'a>(
        &'a self,
        g: &'a Self::Graph,
        s: Option<&Vertex<ChangeId>>,
    ) -> Result<GraphIterator<'a, Self>, TxnErr<Self::GraphError>> {
        Ok(GraphIterator {
            cursor: self.graph_cursor(g, s)?,
            txn: self,
            g: g,
        })
    }

pub struct GraphIterator<'a, T: GraphIter> {
    txn: &'a T,
    g: &'a T::Graph,
    cursor: T::GraphCursor,
}
impl<'a, T: GraphIter> Iterator for GraphIterator<'a, T> {
    type Item = Result<(&'a Vertex<ChangeId>, &'a SerializedEdge), TxnErr<T::GraphError>>;
    fn next(&mut self) -> Option<Self::Item> {
        self.txn.next_graph(self.g, &mut self.cursor)
    }
}

    let mut cursor = txn.iter_graph(&channel, None).unwrap();

    let mut cursor = txn.graph_cursor(&channel, None).unwrap();

    let mut cursor = txn.iter_graph(&channel, None).unwrap();

    let mut cursor = txn.graph_cursor(&channel, None).unwrap();

    fn iter_graph(

    fn graph_cursor(