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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 flat_list(input_list):
 r""" Given a list of nested lists of arbitrary depth, returns a single level or 'flat' list. """

    x = input_list
    if isinstance(x, list):
        return [a for i in x for a in flat_list(i)]
    else:
        return [x]