(define (A x y)
  (cond [(= y 0) 0]
        [(= x 0) (* 2 y)]
        [(= y 1) 2]
        [else (A (- x 1)
                 (A x (- y 1)))]))

; (A 1 10)
; (A 0 (A 1 9))
; (A 0 (A 0 (A 1 8)))
; (A 0 (A 0 (A 0 (A 1 7))))
; (A 0 (A 0 (A 0 (A 0 (A 1 6)))))
; (A 0 (A 0 (A 0 (A 0 (A 0 (A 1 5))))))
; (A 0 (A 0 (A 0 (A 0 (A 0 (A 0 (A 1 4)))))))
; (A 0 (A 0 (A 0 (A 0 (A 0 (A 0 (A 0 (A 1 3))))))))
; (A 0 (A 0 (A 0 (A 0 (A 0 (A 0 (A 0 (A 0 (A 1 2)))))))))
; (A 0 (A 0 (A 0 (A 0 (A 0 (A 0 (A 0 (A 0 (A 0 (A 1 1))))))))))
; (A 0 (A 0 (A 0 (A 0 (A 0 (A 0 (A 0 (A 0 (A 0 2)))))))))
; (A 0 (A 0 (A 0 (A 0 (A 0 (A 0 (A 0 (A 0 4))))))))
; (A 0 (A 0 (A 0 (A 0 (A 0 (A 0 (A 0 8)))))))
; (A 0 (A 0 (A 0 (A 0 (A 0 (A 0 16))))))
; (A 0 (A 0 (A 0 (A 0 (A 0 32)))))
; (A 0 (A 0 (A 0 (A 0 64))))
; (A 0 (A 0 (A 0 128)))
; (A 0 (A 0 256))
; (A 0 512)
; > 1024

; (A 2 4)
; (A 1 (A 2 3))
; (A 1 (A 1 (A 2 2)))
; (A 1 (A 1 (A 1 (A 2 1))))
; (A 1 (A 1 (A 1 2)))
; (A 1 (A 1 (A 0 (A 1 1))))
; (A 1 (A 1 (A 0 2)))
; (A 1 (A 1 4))
; (A 1 (A 0 (A 1 3)))
; (A 1 (A 0 (A 0 (A 1 2))))
; (A 1 (A 0 (A 0 (A 0 (A 1 1)))))
; (A 1 (A 0 (A 0 (A 0 2))))
; (A 1 (A 0 (A 0 4)))
; (A 1 (A 0 8))
; (A 1 16)
; > 2^16 
; > 65536

; (A 3 3)
; (A 2 (A 3 2))
; (A 2 (A 2 (A 3 1)))
; (A 2 (A 2 2))
; (A 2 4)
; > 65536

; (A 2 1) ->        2 -> (expt 2 0))    
; (A 2 2) ->  (A 1 2) -> (A 1 (expt 2 (expt 2 0)))    
; (A 2 3) ->  (A 1 4) -> (A 1 (expt 2 (expt 2 (expt 2 0))))   
; (A 2 4) -> (A 1 16) -> (A 1 (expt 2 (expt 2 (expt 2 (expt 2 0)))))
; (A 2 5) -> (A 1 (expt 2 16)) -> (A 1 (expt 2 (expt 2 (expt 2 (expt 2 (expt 2 0))))))

; (define (f n) (A 0 n)) -> f(n) = 2n
; (define (g n) (A 1 n)) -> g(n) = 2^n
; (define (h n) (A 2 n)) -> h(n) = 2^(h(n - 1))