def words_normalize(words):
    """
    Do a normalization precess on words. In this case is just a tolower(),
    but you can add accents stripping, convert to singular and so on...
    """
    normalized_words = []
    for index, word in words:
        wnormalized = word.lower()
        normalized_words.append((index, wnormalized))
    return normalized_words