WORST_CASE(?,O(n^1))

Solution:
---------

  0 :: [] -(0)-> a(4)
  0 :: [] -(0)-> a(0)
  bits :: [a(4)] -(1)-> a(0)
  half :: [a(4)] -(2)-> a(4)
  s :: [a(4)] -(4)-> a(4)
  s :: [a(0)] -(0)-> a(0)


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

  0 :: [] -(0)-> a_cf(0)
  bits :: [a_cf(0)] -(0)-> a_cf(0)
  half :: [a_cf(0)] -(0)-> a_cf(0)
  s :: [a_cf(0)] -(0)-> a_cf(0)