(define factorial 
   X -> (factorialh X 1))

(define factorialh 
   0 Accum -> Accum 
   X Accum -> (factorialh (- X 1) (* X Accum))) 

(define plus 
   X 0 -> X  
   X Y -> (+ 1 (plus X (- Y 1)))) 

(define fib 
   0 -> 0  
   1 -> 1  
   X -> (+ (fib (- X 1)) (fib (- X 2))))

(define even? 
   1 -> false  
   X -> (odd? (- X 1)))

(define odd?  
   1 -> true  
   X -> (even? (- X 1)))