check-in working versions of series.py and ack.py; need more work on the...

... asserts
It's generally a good practice to place interactive code inside an

    if __name__ == '__main__':

block. This way, the interactive portion will not run if you import this module into another using

    import series

(which you may want to do if you ever want access to these functions without re-writing them), but the interactive portion will still run if you're running the file.