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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 _growing_step_sequence(interval_growth, max_interval, init_interval, start_level=None):
 """ Returns an iterator that constructs a sequence of trigger levels with growing intervals. The interval is growing exponentially until it reaches the maximum value. Then the interval stays the same and the sequence becomes linear. An optional starting level `start_level` defaults to the initial interval. The interval starts out as `init_interval`, multiplied by `interval_growth` in each step until it reaches the `max_interval`. """

        interval = init_interval
        next_level = start_level or init_interval
        while True:
            yield next_level
            interval = min(interval * interval_growth, max_interval)
            next_level += interval