import sys

class BST:

  def __init__(self,left=None,value=None,right=None):
    self._left = left
    self._value = value
    self._right = right

  def empty(self):

  def min(self): 
   
  def max(self): 
   
  def member(self,x):
  
  def height(self):
  
  def size(self):
  
  def insert(self,x):
    
  def delete(self,x):

  def delete_helper(self,x):
  
  def __str__(self):
    return "{ " + self.str_helper().strip(', ') + " }"

  def str_helper(self):
    if self.empty():
      return ""
    else:
      return self._left.str_helper()+str(self._value)+", "+self._right.str_helper()