そもそも
(define (誰かひとりが犯人?  . ls)
    (cond
     ((eq? (car ls) '有罪) (and (eq? (cadr ls) '無罪) (eq? (caddr ls) '無罪)))
     ((eq? (cadr ls) '有罪) (and (eq? (car ls) '無罪) (eq? (caddr ls) '無罪)))
     ((eq? (caddr ls) '有罪) (and (eq? (car ls) '無罪) (eq? (cadr ls) '無罪)))))
の不備は不問？