import copy

def deep_copy_nested_dict(
        nested_dict: dict[str, dict[str, list]]
    ) -> dict[str, dict[str, list]]:
    """
    Create a deep copy of a nested dictionary.
    A deep copy is a new object that is created recursively, copying all
    the collections found in the original dictionary.

    This way, the new dictionary is independent of the original one: if you
    modify the new dictionary, the original dictionary remains unchanged.

    Parameters
    ----------
    nested_dict : dict[str, dict[str, list]]
        A nested dictionary where the inner dictionary may contain
        other collections.

    Returns
    -------
    dict[str, dict[str, list]]
        A deep copy of the nested dictionary.

    Examples
    --------
    >>> nested_dict = {
    ...     'key1': {'innerKey1': [1, 2, 3], 'innerKey2': [4, 5]},
    ...     'key2': {'innerKey3': [6, 7]}
    ... }
    >>> copied_dict = deep_copy_nested_dict(nested_dict)
    >>> assert copied_dict["key1"] is not nested_dict["key1"]
    >>> assert copied_dict["key2"] is not nested_dict["key2"]
    """
    raise NotImplementedError("Complete this function.")