input: def remove_vowels(string: str) -> str:
      """Remove all vowels from the given string.
      >>> remove_vowels("hello world")
      'hll wrld'
      >>> remove_vowels("AEIOUaeiou")
      ''
      """
output:     vowels = "AEIOUaeiou"
      return ''.join([char for char in string if char not in vowels])