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;; Calculation of Hofstadter's male and female sequences as a list of pairs
(define (hofstadter-male-female n)
(letrec ((female (lambda (n)
(if (= n 0)
1
(- n (male (female (- n 1)))))))
(male (lambda (n)
(if (= n 0)
0
(- n (female (male (- n 1))))))))
(let loop ((i 0))
(if (> i n)
'()
(cons (cons (female i)
(male i))
(loop (+ i 1)))))))
(hofstadter-male-female 8)
(define (find-first func lst)
(call-with-current-continuation
(lambda (return-immediately)
(for-each (lambda (x)
(if (func x)
(return-immediately x)))
lst)
#f)))
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