(define (queens board-size) (define (queen-cols k) (if (= k 0) (list empty-board) (filter (lambda (positions) (safe? k positions)) (flatmap (lambda (rest-of-queens) (map (lambda (new-row) (adjoin-position new-row k rest-of-queens)) (enumer…

(define (queens board-size) (define (queen-cols k) (if (= k 0) (list empty-board) (filter (lambda (positions) (safe? k positions)) (flatmap (lambda (rest-of-queens) (map (lambda (new-row) (adjoin-position new-row k rest-of-queens)) (enumer…

(define (equal-sum-of-unique-trio n s) (filter (lambda (l) (= s (+ (car l) (cadr l) (caddr l)))) (flatmap (lambda (i) (flatmap (lambda (j) (map (lambda (k) (list i j k)) (enumerate-interval 1 (- j 1)))) (enumerate-interval 1 (- i 1)))) (en…

(define (unique-pairs n) (flatmap (lambda (i) (map (lambda (j) (list i j)) (enumerate-interval 1 (- i 1)))) (enumerate-interval 1 n))) (define (prime-sum-pairs n) (map make-pair-sum (filter prime-sum? (unique-pairs n))))