(define (normal-reduce f)
  ((lambda (value) (if (equal? value f) f (normal-reduce value)))
   (let r ((f f) (g '()))
     (cond ((not (pair? f))
            (if (null? g) f (if (eq? f (car g)) (cadr g) (r f (caddr
g)))))
           ((and (pair? (car f)) (= 2 (length f)) (eq? 'lambda (caar
f)))
            (r (caddar f) (list (cadar f) (r (cadr f) g) g)))
           ((and (not (null? g)) (= 3 (length f)) (eq? 'lambda (car
f)))
            (cons 'lambda (r (cdr f) (list (cadr f) (delay (cadr f))
g))))
           (else (map (lambda (x) (r x g)) f))))))

car: expects argument of type <pair>; given r