iterator problem

Here is graph.hh
#ifndef GRAPH_HH
#define GRAPH_HH 1

#include <list>
#include <vector>
#include <cstddef>

std::list<int>::iterator it;

template<class NodeData, class EdgeData, typename NodeIndex=size_t>
                                                      class Graph {
public:
    struct Edge {
        NodeIndex lo, hi;
        EdgeData *data;

        Edge() : lo(0), hi(0), data(0) {}
    } ;

    class Node {
        std::list<Edge> edges;
        NodeData *data;
    } ;

    std::list<int >::iterator works;

    int fred;

    std::list<Edge>::iterator help;

private:
    std::vector<Node> nodes;

public:
    Graph(NodeIndex nodesNum) : nodes(nodesNum) {}

    void setNodeData(NodeIndex ni, NodeData *nd)
                            { nodes[ni].data=nd; }
    NodeData *getNodeData(NodeIndex ni) const
                     { return nodes[ni].data; }

} ; // Graph

#endif

Here is the error message when graph-test.cc #includes it
In file included from graph-test.cc:1:
graph.hh:29: error: type ?std::list<Graph<NodeData, EdgeData, NodeIndex>::Edge, std::allocator<Graph<NodeData, EdgeData, NodeIndex>::Edge> >? is not derived from type ?Graph<NodeData, EdgeData, NodeIndex>?
graph.hh:29: error: expected ?;? before ?help?

Note that my first use of iterator works.
What is the matter with std::list<Edge>::iterator
that is not the matter with std::list<int >::iterator ?

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