// Сложный контейнер
class vector_of_lists{
private:
  std::vector< std::list<int> > adj;
public:
  // ... Полезные методы

  // Итератор
  class adjIterator;
  friend class adjIterator;
};

// Итератор к нему
class vector_of_lists::adjIterator{
private:
  const vector_of_lists& G;
  int v;
  std::list<int>::iterator list_it; // ( 1 )
public:
  adjIterator(const vector_of_lists& G, int v): G(G), v(v){
    // ... Какая-то работа
  };

  // Первый элемент
  int begin(){
    list_it = G.adj[v].begin(); // ( 2 )
    return *list_it;
  };

  // ... Полезные методы
};

  void testIterator(){
    std::list<int>::iterator ls_iter;
    std::vector< std::list<int> > adj;
    //...
    ls_iter = adj[ 0 ].begin();
    // ...
  }

2> error C2679: binary '=' : no operator found which takes a right-hand operand of type 'std::list<_Ty>::_Const_iterator<_Secure_validation>' (or there is no acceptable conversion)
2>        with
2>        [
2>            _Ty=int,
2>            _Secure_validation=true
2>        ]
2>        c:\program files\microsoft visual studio 8\vc\include\list(421): could be 'std::list<_Ty>::_Iterator<_Secure_validation> &std::list<_Ty>::_Iterator<_Secure_validation>::operator =(const std::list<_Ty>::_Iterator<_Secure_validation> &)'
2>        with
2>        [
2>            _Ty=int,
2>            _Secure_validation=true
2>        ]
2>        while trying to match the argument list '(std::list<_Ty>::_Iterator<_Secure_validation>, std::list<_Ty>::_Const_iterator<_Secure_validation>)'
2>        with
2>        [
2>            _Ty=int,
2>            _Secure_validation=true
2>        ]