def play_round( decks ):
    """
    Plays a single round of the combat game.
    This function returns the decks after one round.
    """
    cards = [ deck.pop(0) for deck in decks ]
    if cards[0] > cards[1]:
        decks[0] += [ cards[0], cards[1] ]
    elif cards[1] > cards[0]:
        decks[1] += [ cards[1], cards[0] ]
    return decks