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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def mean_area_distance(item_a, item_b, max_value):
 """ Absolute difference in the means of the areas of each track over time. Args: item_a: STObject from the first set in TrackMatcher item_b: STObject from the second set in TrackMatcher max_value: Maximum distance value used as scaling value and upper constraint. Returns: Distance value between 0 and 1. """

    mean_area_a = np.mean([item_a.size(t) for t in item_a.times])
    mean_area_b = np.mean([item_b.size(t) for t in item_b.times])
    return np.abs(mean_area_a - mean_area_b) / float(max_value)