input: 
  def correct_song_definitions(songs: List[Song]) -> bool:
      """ Validates if a list of Song instances are correctly defined, meaning they have
      a title and an artist, and that the eq method returns True if two songs have the same
      title and artist.
      >>> song1 = Song("Bohemian Rhapsody", "Queen")
      >>> song2 = Song("Bohemian Rhapsody", "Queen")
      >>> song3 = Song("Stairway to Heaven", "Led Zeppelin")
      >>> correct_song_definitions([song1, song2, song3])
      True
      """
      return all(song.title and song.artist for song in songs) and \
             all(song1 == song2 for i, song1 in enumerate(songs) for song2 in songs[i+1:])
  
output:     for song in songs:
          if not (song.title and song.artist):
              return False
      for i, song1 in enumerate(songs):
          for song2 in songs[i+1:]:
              if song1.title == song2.title and song1.artist == song2.artist and song1 != song2:
                  return False
      return True