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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 flattened_nested_key_indices(nested_dict):
 """ Combine the outer and inner keys of nested dictionaries into a single ordering. """

    outer_keys, inner_keys = collect_nested_keys(nested_dict)
    combined_keys = list(sorted(set(outer_keys + inner_keys)))
    return {k: i for (i, k) in enumerate(combined_keys)}