def create_inverse_index(index):
    """Return an inverse index mapping the integer indexes to string values.

    For the `index` with mapping ``index[field][v] = i``, the inverse index has mapping ``inverse_index[field][i] = v``.
    See `Instance.to_sentence` method for usage of the inverse index for transformation of instances to sentences.
    """
    return {f: {v: k for k, v in c.items()} for f, c in index.items()}