21b4c336dad121a562bac5fb06df231dc5d1624291eb94cde93d



(define (combination n ls) (cond ((= n 0) '(())) ((null? ls) '()) (else (append (map (lambda (x) (cons (car ls) x)) (combination (- n 1) (cdr ls))) (combination n (cdr ls)))))) (define (reversible? x y) (equal? (string-append x y) (string-append y x)) (define (sol input) (let ((ls (combination 2 input))) (define (loop ls) (cond ((null? ls) (display "true")) ((reversible? (car (car ls)) (car (cdr (car ls)))) (loop (cdr ls))) (else (display "false")))) (loop ls)))


눈치