filterNameSet :: (Name -> Bool) -> NameSet -> NameSet
intersectNameSet :: NameSet -> NameSet -> NameSet
intersectsNameSet :: NameSet -> NameSet -> Bool -- True if non-empty intersection
filterNameSet :: (Name -> Bool) -> NameSet -> NameSet
intersectNameSet :: NameSet -> NameSet -> NameSet
intersectsNameSet :: NameSet -> NameSet -> Bool -- True if non-empty intersection