def get_words_from_string(line):
    """
    Return a list of the words in the given input string,
    converting each word to lower-case.

    Input:  line (a string)
    Output: a list of strings 
              (each string is a sequence of alphanumeric characters)
    """
    word_list = []          # accumulates words in line
    character_list = []     # accumulates characters in word
    for c in line:
        if c.isalnum():
            character_list.append(c)
        elif len(character_list)>0:
            word = "".join(character_list)
            word = word.lower()
            word_list.append(word)
            character_list = []
    if len(character_list)>0:
        word = "".join(character_list)
        word = word.lower()
        word_list.append(word)
    return word_list