SICP 問題 2.65
(define (union-tree s t) (list->tree (union-set (tree->list-2 s) (tree->list-2 t)))) (define (intersection-tree s t) (list->tree (intersection-set-local (tree->list-2 s) (tree->list-2 t))))
(define (union-tree s t) (list->tree (union-set (tree->list-2 s) (tree->list-2 t)))) (define (intersection-tree s t) (list->tree (intersection-set-local (tree->list-2 s) (tree->list-2 t))))