input: 
  from typing import List
  
  def min_max(arr: List[int]) -> List[int]:
      """ Given an array of numbers, return an array with the greatest and smallest values.
      >>> min_max([3, 4, 2, 8, 15, 6])
      [2, 15]
      """
      return [min(arr), max(arr)]
  
output:     return [min(arr), max(arr)]