SICP問題2.57
任意個の項の和と積が扱える変更した和と積の手続き
(define (augend s) (if (null? (cdr (cddr s))) (caddr s) (list (car s) (car (cddr s)) (cadr (cddr s))))) (define (multiplicand p) (if (null? (cdr (cddr p))) (caddr p) (list (car p) (car (cddr p)) (cadr (cddr p)))))