input: from typing import List
  
  
  def to_lower(string: List[str]) -> List[str]:
      """ Convert all characters of a string in lowercase.
      >>> to_lower(["HELLO"])
      ['hello']
      >>> to_lower(["THIS", "IS", "PYTHON"])
      ['this', 'is', 'python']
      """
output:     return [s.lower() for s in string]