(define num-times-range
(lambda (a low high) ; compute a × (low × low+1 × ... × high) as
(if (> low high) ; (a × low) × (low+1 × ... × high)
a
(num-times-range (* a low) (+ low 1) high))))
The factorial of n is just an instance of P on previous slide:
1 × (1 × ... × n)
Use num-times-range to write factorial with one argument:
(define factorial
(lambda (n)
_____________________))