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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 nested_update(d, u):
 """Merge two nested dicts. Nested dicts are sometimes used for representing various recursive structures. When updating such a structure, it may be convenient to present the updated data as a corresponding recursive structure. This function will then apply the update. Args: d: dict dict that will be updated in-place. May or may not contain nested dicts. u: dict dict with contents that will be merged into ``d``. May or may not contain nested dicts. """

    for k, v in list(u.items()):
        if isinstance(v, collections.Mapping):
            r = nested_update(d.get(k, {}), v)
            d[k] = r
        else:
            d[k] = u[k]
    return d