def _publications_urls(request, analyses):
    """Return set of publication URLS for given analyses.

    Parameters
    ----------
    request
        HTTPRequest
    analyses
        seq of Analysis instances
    Returns
    -------
    Set of absolute URLs (strings)
    """
    # Collect publication links, if any
    publication_urls = set()
    for a in analyses:
        surface = a.related_surface
        if surface.is_published:
            pub = surface.publication
            pub_url = request.build_absolute_uri(pub.get_absolute_url())
            publication_urls.add(pub_url)
    return publication_urls