diff --git a/doc/notes-on-hll.md b/doc/notes-on-hll.md
index aada9a3..fd15a79 100644
--- a/doc/notes-on-hll.md
+++ b/doc/notes-on-hll.md
@@ -42,3 +42,22 @@ and `I` needs to be clarified, among many other things.
 
     (define-syntax-rule (forever O ...)
 	  (until (rising-edge #f) O ...))
+
+## Examples
+
+```racket
+#lang prospect/actor
+;; Simple mutable box and count-to-infinity box client.
+
+(struct set-box (new-value) #:transparent)
+(struct box-state (value) #:transparent)
+
+(actor (forever #:collect [(value 0)]
+         (assert (box-state value))
+         (on (message (set-box $new-value))
+           new-value)))
+
+(actor (forever
+         (on (asserted (box-state $value))
+           (send! (set-box (+ value 1))))))
+```
diff --git a/prospect/examples/box-and-client.rkt b/prospect/examples/box-and-client.rkt
new file mode 100644
index 0000000..e766c5f
--- /dev/null
+++ b/prospect/examples/box-and-client.rkt
@@ -0,0 +1,26 @@
+#lang prospect
+;; Simple mutable box and count-to-infinity box client.
+
+(struct set-box (new-value) #:transparent)
+(struct box-state (value) #:transparent)
+
+(spawn (lambda (e current-value)
+         (match e
+           [(message (set-box new-value))
+            (transition new-value (patch-seq (retract (box-state current-value))
+                                             (assert (box-state new-value))))]
+           [_ #f]))
+       0
+       (sub (set-box ?))
+       (assert (box-state 0)))
+
+(spawn (lambda (e s)
+         (match e
+           [(patch added removed)
+            (transition s (for/list [(v (matcher-project/set/single
+                                         added
+                                         (compile-projection (box-state (?!)))))]
+                            (message (set-box (+ v 1)))))]
+           [_ #f]))
+       (void)
+       (sub (box-state ?)))