/**
    * public String min()
    *
    * Returns the info of the item with the smallest key in the tree,
    * or null if the tree is empty
    */
   public String min()
   {
	   if(this.empty())
		   return null;
	   IWAVLNode pos = this.root;
	   while(pos.getLeft().isRealNode())
		   pos = pos.getLeft();
	   return pos.getValue();
   }