public boolean isBinarySearchTree(){
	if(isEmpty()|| isLeaf())
	  return true;
					
	Comparable rootKey = (Comparable) key;
		
	if(left.isGreater(rootKey) && right.isLess(rootKey))
	    return left.isBinarySearchTree() && right.isBinarySearchTree();
	else
	    return false;
     }


    // returns true if rootKey is less than all keys in the invoking tree; otherwise false
    private boolean isLess(Comparable rootKey)
    {
    	if(isEmpty())
    	   return true;
    	
    	if(rootKey.compareTo((Comparable)key) >= 0)
    	   return false;	
        else		
    	  return getRight().isLess(rootKey) && getLeft().isLess(rootKey);
    }
    

    // returns true if root key is greater than all keys in the invoking tree
    private boolean isGreater(Comparable rootKey)
    {
    	if(isEmpty())
    	   return true;
    		
    
    	if(rootKey.compareTo((Comparable)key) <= 0)
    	   return false;
    	else				
    	   return getRight().isGreater(rootKey) && getLeft().isGreater(rootKey);
    }