The Ackermann function implemented using Dylan

Description from:
  http://www.astro.virginia.edu/~eww6n/math/AckermannFunction.html

The Ackermann function is the simplest example of a well-defined Total
Function which is Computable but not Primitive Recursive, providing a
counterexample to the belief in the early 1900s that every Computable
Function was also Primitive Recursive (Dtzel 1991). It grows faster
than an exponential function, or even a multiple exponential function.