WORST_CASE(?,O(n^1))

Solution:
---------

  0 :: [] -(0)-> a(1)
  p :: [a(1) x a(1) x a(1)] -(1)-> a(0)
  s :: [a(1)] -(1)-> a(1)


Cost Free Signatures:
---------------------

  0 :: [] -(0)-> a_cf(0)
  p :: [a_cf(0) x a_cf(0) x a_cf(0)] -(0)-> a_cf(0)
  s :: [a_cf(0)] -(0)-> a_cf(0)