SICP exercise 1.11

Exercise 1.11. 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 that computes f by means of a recursive process.


(define (f n)
    (cond ((< n 3) n)
    (else ((+ (f (- n 1))
            (*
                (f (- n 2)) 2)
            (*
                (f (- n 3)) 3))))))

It gives me "The object 4 is not applicable".
Can you guys help me?

Shiichan is pretty terrible.  Here is the correct URL: http://groups.csail.mit.edu/mac/classes/6.001/abelson-sussman-lectures/