combineS :: Eq a => TraverseKind -> Op2 (Skel a)
combineS = \case
  ParK -> unknownS
  TenK -> mappend
  SeqK -> dotS
combineS :: Eq a => TraverseKind -> Op2 (Skel a)
combineS = \case
  ParK -> unknownS
  TenK -> mappend
  SeqK -> dotS
combineS = \case
  ParK -> unknownS
  TenK -> mappend
  SeqK -> dotS