input: def encode_message(text):
      """
      Write a python function that receives a text, and transforms it by 
      swapping the case of all letters and substituting all vowels with the 
      letter that appears two positions ahead in the English alphabet.
      Assume the text contains only letters.
  
      Examples:
      >>> encode_message('test')
      'TGST'
      >>> encode_message('This is a message')
      'tHKS KS C MGSSCGG'
      """
output:     vowels = 'aeiouAEIOU'
      vowel_map = {c: chr(ord(c) + 2) for c in vowels}
      transformed_text = []
  
      for char in text:
          if char in vowels:
              transformed_text.append(vowel_map[char])
          elif char.isalpha():
              transformed_text.append(char.swapcase())
          else:
              transformed_text.append(char)
  
      return ''.join(transformed_text)