(define (double f)
(lambda (x) (f (f x))))
The example given can be expanded in the following way:
(((double (double double)) inc) 5) (((double (lambda (x) (double (double x)))) inc) 5) ; ... similar expansion omitted ((double (double (double (double inc)))) 5) ((double (double (double (lambda (x) (inc (inc x)))))) 5) ; ... similar expansion omitted (inc (inc (inc (inc (inc (inc (inc (inc (inc (inc (inc (inc (inc (inc (inc (inc 5)))))))))))))))) ; ... reduction omitted ;21
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