def simplify_provenance(proxy):
    """If there are multiple dates given for some of the provenance
    fields, we can logically conclude which one is the most meaningful."""
    for prop_name in ['modifiedAt', 'retrievedAt']:
        if proxy.has(prop_name, quiet=True):
            values = proxy.get(prop_name)
            proxy.set(prop_name, max(values))
    for prop_name in ['authoredAt', 'publishedAt']:
        if proxy.has(prop_name, quiet=True):
            values = proxy.get(prop_name)
            proxy.set(prop_name, min(values))
    return proxy
