text: def falling(n, k):
      """Compute the falling factorial of n to depth k.
  
      >>> falling(6, 3)  # 6 * 5 * 4
      120
      >>> falling(4, 3)  # 4 * 3 * 2
      24
      >>> falling(4, 1)  # 4
      4
      >>> falling(4, 0)
      1
      """
      "*** YOUR CODE HERE ***"
      i = 0
      ans = 1
      while i<k:
          ans = ans * n
          n,i=n-1,i+1
      return ans
  
  
  def sum_digits(y):
      """Sum all the digits of y.
  
      >>> sum_digits(10) # 1 + 0 = 1
      1
      >>> sum_digits(4224) # 4 + 2 + 2 + 4 = 12
      12
      >>> sum_digits(1234567890)
      45
      >>> a = sum_digits(123) # make sure that you are using return rather than print
      >>> a
      6
      """
      "*** YOUR CODE HERE ***"
      ans = 0
      while y:
          ans +=y%10
          y = y//10
      return ans
  
  
  def double_eights(n):
      """Return true if n has two eights in a row.
      >>> double_eights(8)
      False
      >>> double_eights(88)
      True
      >>> double_eights(2882)
      True
      >>> double_eights(880088)
      True
      >>> double_eights(12345)
      False
      >>> double_eights(80808080)
      False
      """
      "*** YOUR CODE HERE ***"
      i = 0
      while n:
          if n%10==8:
              i+=1
          if i>0 and n%10!=8:
              i=0
          if i==2:
              return True
          n = n//10
      return False
  