-- Nov 17 In-Class Exercise Thread
(define (fib-helper n1 n2 prev1 prev2)
(if (< n1 2) 1
(if (< n1 4) n1
(if (= n1 n2) (+ prev1 prev2)
(if (= n2 3) (fib-helper n1 (+ n2 1) 3 2)
(fib-helper n1 (+ n2 1) (+ prev1 prev2) prev1))))))
(define (fib n)
(fib-helper n 0 0 0))
(fib 5)
<nowiki> (define (fib-helper n1 n2 prev1 prev2)
(if (< n1 2) 1
(if (< n1 4) n1
(if (= n1 n2) (+ prev1 prev2)
(if (= n2 3) (fib-helper n1 (+ n2 1) 3 2)
(fib-helper n1 (+ n2 1) (+ prev1 prev2) prev1))))))
(define (fib n)
(fib-helper n 0 0 0))
(fib 5)</nowiki>