removePlusses (Appl f ps) = S.map (Appl f) (traverseSet removePlusses ps)
  where traverseSet f s = S.fromList (traverse (S.toList . f) s)
removePlusses (Appl f ps) = S.map (Appl f) (traverseSet removePlusses ps)
  where traverseSet f s = S.fromList (traverse (S.toList . f) s)
removePlusses (Appl f ps) = S.map (Appl f) (traverseSet removePlusses ps)
  where traverseSet f s = S.fromList (traverse (S.toList . f) s)