diff --git a/demo/real.dee b/demo/real.dee
index d40875a..4509197 100644
--- a/demo/real.dee
+++ b/demo/real.dee
@@ -8,3 +8,12 @@ fizzbuzz <- ->
   )
 
 fizzbuzz()
+
+print()
+
+ack <- m -> n ->
+  if m = 0 n + 1
+  elif n = 0 ack(m - 1, 1)
+  else ack(m - 1, ack(m, n - 1))
+
+print(ack(3, 4)) ## 125