       "2000-02-29T23:00:07"
 
   """
-  @spec to_iso8601(Calendar.naive_date_time) :: String.t
+  @spec to_iso8601(Calendar.naive_datetime) :: String.t
   def to_iso8601(naive_datetime)
 
   def to_iso8601(%{year: year, month: month, day: day,

      iex> DateTime.to_iso8601(dt)
      "2000-02-29T23:00:07-04:00"
  """
  @spec to_iso8601(Calendar.date_time) :: String.t
  def to_iso8601(datetime)

  def to_iso8601(%{calendar: Calendar.ISO, year: year, month: month, day: day,

      "2000-02-29 23:00:07"

  """
  @spec to_string(Calendar.naive_datetime) :: String.t
  def to_string(naive_datetime)

  def to_string(%{calendar: calendar, year: year, month: month, day: day,
