The Child SLLIST:

class VOID_SLLIST : public VOID_LIST_CORE{
    friend class VOID_SL_CELL;
    friend class VOIDSLLISTFIter;
  public:
    VOID_SLLIST(ACCESS_VOID *element_access_in);
    VOID_SLLIST(VOID_SLLIST&);
    ~VOID_SLLIST();
    VOID_SLLIST& operator=(const VOID_SLLIST&);
    // agents
    int is_empty(){return(head==NULL);};
    void delete_element(Arbent target_key);
    void search_element(Arbent search_key);
    //Arbent build_list(VOID_VECTOR& A);
    int get_number_elements();
    void insert_after(Arbent before_element,Arbent new_element);
    void insert_before(Arbent after_element,Arbent new_element);
    void mergesort();
    istream& grab(istream& in);
    ostream& print(ostream& out) const;
  protected:
    VOID_SL_CELL *head;
    VOID_SL_CELL* get_element_address(Arbent search_key);
    VOID_SL_CELL* get_before_element_address(Arbent search_key);
    VOID_SL_CELL* get_after_element_address(Arbent search_key);
  };