}
// Provide global definitions of external depth first iterators...
-template <class T, class SetTy>
+template <class T, class SetTy = std::set<typename GraphTraits<T>::NodeType*> >
struct df_ext_iterator : public df_iterator<T, SetTy, true> {
df_ext_iterator(const df_iterator<T, SetTy, true> &V)
: df_iterator<T, SetTy, true>(V) {}