class AuxObserver : private CombinationObserver
    {
        CombinatoryPolicy* const sub_policy;
        Avs initialComb;
        AuxObserver* nextObs;
        CombinationObserver* observed_by;   //! ultimo observador

        virtual void update (const Avs* t)
        {
            // aca se hace la union entre initialComb y t
            nextObs->combine(union(initialComb, *t);
        }

    public:
        //! Constructor
        AuxObserver(CombinatoryPolicy* comb, const Avs& elements, CombinationObserver* observed_by): nextComb(comb), elements(elements), lastComb(), nextObs(NULL), observed_by(observed_by)
        {}

        inline void set_next_obs (AuxObserver* obs);

        void combine(const Avs& init)
        {
            initialComb = init;  (podria ser un puntero)
            sub_policy->combine();  // no lleva mas el param.; invoca this->update
        }
    };