<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def nested_set_dict(d, keys, value):
 """Set a value to a sequence of nested keys Parameters d: Mapping keys: Sequence[str] value: Any """

    assert keys
    key = keys[0]
    if len(keys) == 1:
        if key in d:
            raise ValueError("duplicated key '{}'".format(key))
        d[key] = value
        return
    d = d.setdefault(key, {})
    nested_set_dict(d, keys[1:], value)