n :: RefHistory -> RefKey -> Int
lastMention st (c,i) =
    sum . Map.elems . rhCount $ supersetMentions (mkSingletonDu (c,i)) st

-- | @la
lastMention :: RefHistory -> RefKey -> Int
lastMention st (c,i) =
    sum . Map.elems . rhCount $ supersetMentions (mkSingletonDu (c,i)) st
lastMention st (c,i) =
    sum . Map.elems . rhCount $ supersetMentions (mkSingletonDu (c,i)) st