1 (define (make-table)
2   (define local-table '())
3   (define make-record cons)
4   (define key-record car)
5   (define value-record cdr)
6   (define (make-tree entry left right) 
7     (list entry let right)) 
8   (define entry car)
9   (define left-branch cadr)
10   (define right-branch caddr)
11   (define key=? equal?)
12   (define (list<? l1 l2)
13     (andmap key<? l1 l2))
14   (define (key<? key1 key2)
15     (cond ((and (string? key1)
16 		(string? key2)) (string<? key1 key2))
17 	  ((and (number? key1)
18 		(number? key2)) (< key1 key2))
19 	  ((and (char? key1)
20 		(char? key2)) (char<? key1 key2))
21 	  (else (error "Unsupported key types -- KEY<?" key1 key2))))
22   (define (element-of-set? x set)
23     (cond ((null? set) false)
24 	  ((key=? (key-record x) (key-record (entry set))) true)
25 	  ((key<? (key-record x) (key-record (entry set))) 
26 	   (element-of-set? x (left-branch set)))
27 	  (else
28 	   (element-of-set? x (right-branch set)))))
29