Update 5B.scm

Author: felipap

code/5B.scm

@@ -38,16 +38,16 @@ Implementing a Primitive
 (define (inverter in out)
 	(define (invert-in)
 		((let
-			((now (logical not (get-signal in))))
+			((now (logical-not (get-signal in))))
 			(after-delay inverter-delay
 				(lambda ()
 					(set-signal! out now))))))
 	(add-action! in invert-in))
 
 (define (logical-not s)
 	(cond
-		((- s 0) 1)
-		((- s 1) 0)
+		((= s 0) 1)
+		((= s 1) 0)
 		(else
 			(error "invalid signal" s))))
 ;# END SLIDE
@@ -258,4 +258,4 @@ QUEUE
 
 (define (set-cdr! x)
 	(x (lambda (a d sa sd) (sd y))))
-;# END SLIDE
+;# END SLIDE