strictlyOrdOL (Snoc as a) (Snoc bs b) =
  compare a b `mappend` strictlyOrdOL as bs
strictlyOrdOL (Snoc as a) (Snoc bs b) =
  compare a b `mappend` strictlyOrdOL as bs
strictlyOrdOL (Snoc as a) (Snoc bs b) =
  compare a b `mappend` strictlyOrdOL as bs