diff --git a/networks.rkt b/networks.rkt
index 48640ee..d8842ff 100644
--- a/networks.rkt
+++ b/networks.rkt
@@ -13,7 +13,10 @@
 
    (struct-out network) Network
    make-same-domains make-boolean-domains make-boolean-network
-   make-01-domains make-01-network update)
+   make-01-domains make-01-network update
+
+   UpdateFunctionForm
+   )
 
   (define-type (State a) (VariableMapping a))
   (define-type (UpdateFunction a) (-> (State a) a))
@@ -113,6 +116,8 @@
                     #hash((x1 . #f) (x2 . #f)))
       (check-equal? (update bn (hash 'x1 #f 'x2 #f) '(x1 x2))
                     #hash((x1 . #f) (x2 . #t)))))
+
+  (define-type UpdateFunctionForm Any)
   )
 
 (require 'typed)
@@ -281,9 +286,6 @@
 ;;; Syntactic description of networks
 ;;; =================================
 
-;;; An update function form is any form which can appear as a body of
-;;; a function and which can be evaluated with eval.  For example,
-;;; '(and x y (not z)) or '(+ 1 a (- b 10)).
 (define update-function-form? any/c)
 
 ;;; A network form consists of a mapping from variables to the forms
diff --git a/scribblings/networks.scrbl b/scribblings/networks.scrbl
index 6d89386..2c4d797 100644
--- a/scribblings/networks.scrbl
+++ b/scribblings/networks.scrbl
@@ -194,6 +194,21 @@ Given a state @racket[s] updates all the variables of @racket[network] from
 
 @section{Syntactic description of networks}
 
+@deftype[UpdateFunctionForm]{
+
+An update function form is any form which can appear as a body of a function
+and which can be evaluated with @racket[eval].
+
+@ex[
+(ann '(and x y (not z)) UpdateFunctionForm)
+(ann '(+ 1 a (- b 10)) UpdateFunctionForm)
+]
+
+@racket[UpdateFunctionForm] is a synonym of @racket[Any].
+
+}
+
+
 @section{Inferring interaction graphs}
 
 This section provides inference of both unsigned and signed interaction graphs.