* \brief Insert the given element into the component of the others.

      *

      * This methods insert the element \e a into the component of the

      * element \e comp. 

      */

     void insert(const T &a, const T &comp) {

       IIter clit = _find(m[comp]);

       ItemList &c = *clit->my_class;

       c.push_back(ItemType(a,0));

       IIter ai = c.end();

       --ai;

       ai->parent = clit;

       m.set(a, ai);

       ++clit->size;

     }

     /**

     }

     /**

      * \brief Move the given element to an other component.

      *

      * This method moves the element \e a from its component

      * to the component of \e comp.

      * If \e a and \e comp are in the same component then

      * it returns false otherwise it returns true.

      */

     bool move(const T &a, const T &comp) {

       IIter ai = m[a];

       IIter lai = _find(ai);

       IIter clit = _find(m[comp]);

       if (lai == clit)

 	return false;

       ItemList &c = *clit->my_class;

       bool is_leader = (lai == ai);

       bool singleton = false;

       if (is_leader) {

 	++lai;

       }

       c.splice(c.end(), *lai->my_class, ai);

       if (is_leader) {

 	if (ai->size == 1) {

 	  classes.erase(ai->my_class);

 	  singleton = true;

 	}

 	else {

 	  lai->size = ai->size; 

 	  lai->my_class = ai->my_class;	

 	}

       }

       if (!singleton) {

 	for (IIter i = lai; i != lai->my_class->end(); ++i)

 	  i->parent = lai;

 	--lai->size;

       }

       ai->parent = clit;

       ai->my_class = 0;

       ++clit->size;

       return true;