template<typename T>
class VertexList
{
    public:
        class iterator:
            public std::list<std::pair<Vertex<T>, VertexList<T> *> >::iterator
        {
            public:
                VertexList<T> operator*();
        };
        // ...
        iterator begin()
        {
            return data.begin();
        }
    private:
        std::list<std::pair<Vertex<T>, VertexList<T> *> > data;

};