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Iterative and recursive processes
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A function f is defined by the rule that f(n) = n if n < 3 and f(n) = f(n - 1) + 2f(n - 2) + 3f(n - 3) if n ≥ 3. Write a procedure f that computes f by means of a recursive process. Write a procedure f-iter that computes f by means of an iterative process.

```
(check-equal? (f 5) 11)
(check-equal? (f-iter 5) 11)
(check-equal? (f 3) 3)
(check-equal? (f-iter 1) 1)
```