def _getobsfate(successorssets):
    """ Compute a changeset obsolescence fate based on its successorssets.
    Successors can be the tipmost ones or the immediate ones. This function
    return values are not meant to be shown directly to users, it is meant to
    be used by internal functions only.
    Returns one fate from the following values:
    - pruned
    - diverged
    - superseded
    - superseded_split
    """
    if len(successorssets) == 0:
        return b'pruned'
    elif len(successorssets) > 1:
        return b'diverged'
    else:
        successors = successorssets[0]
        if len(successors) == 1:
            return b'superseded'
        else:
            return b'superseded_split'
