( append '(b c d) '(a) )
(cons 'b (append '(c d) '(a)) )
(cons 'b '(c d a) )
'(b c d a)
(define (append x z)
(cond ((null? x) z)
(else (cons (car x) (append (cdr x) z))) ))
( append '(b c d) '(a) )の評価は'(b c d a)