diff --git a/os2-example.rkt b/os2-example.rkt
index dca2360..009ef43 100644
--- a/os2-example.rkt
+++ b/os2-example.rkt
@@ -26,7 +26,7 @@
 			    (transition 'no-state (kill)))))))
 
 (define spy
-  (lambda ()
+  (lambda (spy-pid)
     (define (hs label)
       (define ((w kind) . args) (write `(,label ,kind ,@args)) (newline) values)
       (handlers (w 'presence)
@@ -36,9 +36,9 @@
       (add-role (topic-publisher (wild) #:virtual? #t) (hs 'subscriber->publisher))
       (add-role (topic-subscriber (wild) #:virtual? #t) (hs 'publisher->subscriber)))))
 
-(ground-vm (lambda ()
+(ground-vm (lambda (boot-pid)
 	     (transition 'no-state
 	       (spawn spy)
-	       (spawn (lambda () (example-process 1000)))
-	       (spawn (lambda () (example-process 2000)))
+	       (spawn (lambda (pid) (example-process 1000)))
+	       (spawn (lambda (pid) (example-process 2000)))
 	       (kill))))
diff --git a/os2.rkt b/os2.rkt
index 2c7efbd..700e67a 100644
--- a/os2.rkt
+++ b/os2.rkt
@@ -101,7 +101,7 @@
 (struct add-role (topics handlers k) #:prefab)
 (struct delete-role (eid reason) #:prefab)
 (struct send-message (topic body) #:prefab)
-(struct spawn (thunk k) #:prefab)
+(struct spawn (main k) #:prefab)
 (struct kill (pid reason) #:prefab)
 
 ;; An Action is either a Preaction or an (at-meta-level Preaction).
@@ -151,7 +151,7 @@
 (define (make-transition state . actions) (transition state actions))
 (define (make-add-role topics handlers [k #f]) (add-role topics handlers k))
 (define (make-delete-role eid [reason #f]) (delete-role eid reason))
-(define (make-spawn thunk [k #f]) (spawn thunk k))
+(define (make-spawn main [k #f]) (spawn main k))
 (define (make-kill [pid #f] [reason #f]) (kill pid reason))
 
 (define (extend-transition t . more-actions)
@@ -250,7 +250,7 @@
     [(add-role topics hs k) (do-subscribe pid (ensure-topic-union topics) hs k state)]
     [(delete-role eid reason) (do-unsubscribe pid eid reason state)]
     [(send-message topic body) (route-and-deliver topic body state)]
-    [(spawn thunk k) (do-spawn pid thunk k state)]
+    [(spawn main k) (do-spawn pid main k state)]
     [(kill pid-to-kill reason) (do-kill (or pid-to-kill pid) reason state)]))
 
 (define (do-subscribe pid topics hs k state)
@@ -348,12 +348,12 @@
 	       message-topic
 	       body)))
 
-(define (do-spawn spawning-pid thunk k state)
+(define (do-spawn spawning-pid main k state)
+  (define new-pid (vm-next-process-id state))
   (match-define (transition initial-state initial-actions)
     (cond
-     [(procedure? thunk) (send-to-user (lambda (e) (transition #f (kill #f e))) thunk)]
-     [(transition? thunk) thunk]))
-  (define new-pid (vm-next-process-id state))
+     [(procedure? main) (send-to-user (lambda (e) (transition #f (kill #f e))) main new-pid)]
+     [(transition? main) main]))
   (define spawned-state
     (struct-copy vm (enqueue-actions state new-pid initial-actions)
 		 [processes (hash-set (vm-processes state)
@@ -414,8 +414,8 @@
 	       (wrap-trapk pid k))]
     [(? delete-role?) preaction]
     [(? send-message?) preaction]
-    [(spawn thunk k)
-     (spawn thunk (wrap-trapk pid k))]
+    [(spawn main k)
+     (spawn main (wrap-trapk pid k))]
     [(? kill?) preaction]))
 
 (define (nested-vm boot)