diff --git a/os-big-bang-example.rkt b/os-big-bang-example.rkt
index 5ddade1..2a06f8b 100644
--- a/os-big-bang-example.rkt
+++ b/os-big-bang-example.rkt
@@ -37,37 +37,39 @@
 			     (send-message `(tick ,counter ,now))
 			     (loop now (+ counter 1)))]))))
 
-(ground-vm
- (os-big-bang 'none
-	      (subscribe 'display-driver display-driver-handler)
-	      (subscribe 'read-line-driver read-line-driver-handler)
-	      (tick-driver 'ticker 1000)
-	      (send-message `(display "Hello! "))
-	      (send-message 'greet-loop)
-	      (subscribe 'greet-loop-handler
-			 (message-handlers w
-			  ['greet-loop
-			   (transition w
-				       (send-message `(display "Enter your name:\n"))
-				       (send-message `(request read-name read-line)))]))
-	      (subscribe 'ticker-handler
-			 (message-handlers w
-			  [`(tick ,counter ,_)
-			   (transition w
-				       (send-message
-					`(display ,(string-append "TICK "
-								  (number->string counter)
-								  "\n"))))]))
-	      (subscribe 'read-line-result-handler
-			 (message-handlers w
-			  [`(reply read-name ,(== eof))
-			   (transition w
-				       (send-message `(display "Goodbye!\n")))]
-			  [`(reply read-name ,name)
-			   (transition w
-				       (send-message `(display "Hello, "))
-				       (send-message `(display ,name))
-				       (send-message `(display "!\n"))
-				       (unsubscribe 'ticker)
-				       (send-message 'greet-loop)
-				       )]))))
+(define main
+  (os-big-bang 'none
+	       (subscribe 'display-driver display-driver-handler)
+	       (subscribe 'read-line-driver read-line-driver-handler)
+	       (tick-driver 'ticker 1000)
+	       (send-message `(display "Hello! "))
+	       (send-message 'greet-loop)
+	       (subscribe 'greet-loop-handler
+			  (message-handlers w
+			   ['greet-loop
+			    (transition w
+					(send-message `(display "Enter your name:\n"))
+					(send-message `(request read-name read-line)))]))
+	       (subscribe 'ticker-handler
+			  (message-handlers w
+			   [`(tick ,counter ,_)
+			    (transition w
+					(send-message
+					 `(display ,(string-append "TICK "
+								   (number->string counter)
+								   "\n"))))]))
+	       (subscribe 'read-line-result-handler
+			  (message-handlers w
+			   [`(reply read-name ,(== eof))
+			    (transition w
+					(send-message `(display "Goodbye!\n")))]
+			   [`(reply read-name ,name)
+			    (transition w
+					(send-message `(display "Hello, "))
+					(send-message `(display ,name))
+					(send-message `(display "!\n"))
+					(unsubscribe 'ticker)
+					(send-message 'greet-loop)
+					)]))))
+
+(ground-vm main)