WORST_CASE(?,O(n^2))

Solution:
---------

  @ :: [b(1, 0) x b(0, 0)] -(3)-> b(0, 0)
  dd :: [a(0, 0) x b(1, 0)] -(1)-> b(1, 0)
  dd :: [a(0, 15) x b(15, 15)] -(15)-> b(0, 15)
  dd :: [a(0, 0) x b(0, 0)] -(0)-> b(0, 0)
  dd :: [a(0, 1) x b(1, 1)] -(1)-> b(0, 1)
  nil :: [] -(0)-> b(1, 0)
  nil :: [] -(0)-> b(0, 15)
  nil :: [] -(0)-> b(7, 7)
  nil :: [] -(0)-> b(7, 15)
  rev :: [b(0, 15)] -(4)-> b(0, 0)


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

  @ :: [b_cf(0, 0) x b_cf(0, 0)] -(0)-> b_cf(0, 0)
  @ :: [b_cf(2, 0) x b_cf(10, 0)] -(0)-> b_cf(2, 0)
  dd :: [a_cf(0, 0) x b_cf(0, 0)] -(0)-> b_cf(0, 0)
  dd :: [a_cf(0, 0) x b_cf(15, 0)] -(15)-> b_cf(15, 0)
  dd :: [a_cf(0, 0) x b_cf(2, 0)] -(2)-> b_cf(2, 0)
  dd :: [a_cf(0, 0) x b_cf(12, 0)] -(12)-> b_cf(12, 0)
  nil :: [] -(0)-> b_cf(0, 0)
  nil :: [] -(0)-> b_cf(15, 0)
  nil :: [] -(0)-> b_cf(3, 3)
  nil :: [] -(0)-> b_cf(2, 0)
  nil :: [] -(0)-> b_cf(15, 15)
  rev :: [b_cf(15, 0)] -(5)-> b_cf(2, 0)


Base Constructors:
------------------
  dd_b :: [a(0, 0) x b(1, 0)] -(1)-> b(1, 0)
  dd_b :: [a(0, 1) x b(1, 1)] -(1)-> b(0, 1)
  nil_b :: [] -(0)-> b(1, 0)
  nil_b :: [] -(0)-> b(0, 1)