def format_result(word_next_word):
    """
    Converts to string a tuple (word, most_likely_successor)
    word_next_word: tuple (word, most_likely_successor)
    return: string "word: most_likely_successor"
    """
    (word, most_likely_successor) = word_next_word
    return "{}: {}".format(word, most_likely_successor)