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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 flatten(source, task_limit=None):
 """Given an asynchronous sequence of sequences, generate the elements of the sequences as soon as they're received. The sequences are awaited concurrently, although it's possible to limit the amount of running sequences using the `task_limit` argument. Errors raised in the source or an element sequence are propagated. """

    return base_combine.raw(
        source, task_limit=task_limit, switch=False, ordered=False)