WORST_CASE(?,O(n^1))

Solution:
---------

  + :: [A(0) x A(0)] -(0)-> A(0)
  0 :: [] -(0)-> A(1)
  0 :: [] -(0)-> A(0)
  s :: [A(1)] -(1)-> A(1)
  s :: [A(0)] -(0)-> A(0)
  sum :: [A(1)] -(1)-> A(0)
  sum1 :: [A(1)] -(1)-> A(0)


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

  + :: [A_cf(0) x A_cf(0)] -(0)-> A_cf(0)
  0 :: [] -(0)-> A_cf(0)
  s :: [A_cf(0)] -(0)-> A_cf(0)
  sum :: [A_cf(0)] -(0)-> A_cf(0)
  sum1 :: [A_cf(0)] -(0)-> A_cf(0)