diff --git a/scribblings/tbn.scrbl b/scribblings/tbn.scrbl
index 4dc464b..80a3fa1 100644
--- a/scribblings/tbn.scrbl
+++ b/scribblings/tbn.scrbl
@@ -26,6 +26,8 @@
 
 @defmodule[(submod dds/tbn typed)]
 
+@section{TBFs and states}
+
 This module defines threshold Boolean networks (TBN), as well as sign
 Boolean networks (SBN).  The update functions in such networks are
 respectively @seclink["tbf" #:doc '(lib