input: 
  
  def monotonic(l: list):
      """Return True is list elements are monotonically increasing or decreasing.
      >>> monotonic([1, 2, 4, 20])
      True
      >>> monotonic([1, 20, 4, 10])
      False
      >>> monotonic([4, 1, 0, -10])
      True
      """
  
output:     increasing = all(l[i] <= l[i + 1] for i in range(len(l) - 1))
      decreasing = all(l[i] >= l[i + 1] for i in range(len(l) - 1))
      return increasing or decreasing