-- | A discourse unit that would refer to just an element
mkSingletonDu :: RefKey -> DiscourseUnit
mkSingletonDu (c,i) = Node (RefGroup c (Set.singleton i) emptyBounds) []
mkSingletonDu :: RefKey -> DiscourseUnit
mkSingletonDu (c,i) = Node (RefGroup c (Set.singleton i) emptyBounds) []
mkSingletonDu (c,i) = Node (RefGroup c (Set.singleton i) emptyBounds) []