diff --git a/scribblings/tbn.scrbl b/scribblings/tbn.scrbl
index a2be9d7..539579f 100644
--- a/scribblings/tbn.scrbl
+++ b/scribblings/tbn.scrbl
@@ -45,3 +45,28 @@ inputs of the TBF must match the number of variables in the state.
 (require "functions.rkt")
 (apply-tbf-to-state (tbf #(1 1) 1) (hash 'x1 0 'x2 1))
 ]}
+
+@defstruct*[tbf/state ([weights (VariableMapping Real)]
+		       [threshold Real])]{
+
+A state TBF is a @racket[TBF] with named inputs.  A state TBF can be
+applied to states in an unambiguous ways.
+
+}
+
+@deftype[TBF/State]{
+
+The type of the instances of @racket[tbf/state].
+
+}
+
+@deftogether[(@defproc[(tbf/state-w [tbfs TBF/State]) (VariableMapping Real)]
+	      @defproc[(tbf/state-θ [tbfs TBF/State]) Real])]{
+
+Shorter synonyms for field accessors of @racket[tbf/state].
+
+@ex[
+(let ([tbfs (tbf/state (hash 'a 1 'b 1) 1)])
+  (values (tbf/state-w tbfs)
+          (tbf/state-θ tbfs)))
+]}
diff --git a/tbn.rkt b/tbn.rkt
index 2927eb0..34f9625 100644
--- a/tbn.rkt
+++ b/tbn.rkt
@@ -14,6 +14,8 @@
 
   (provide
    apply-tbf-to-state
+
+   (struct-out tbf/state) TBF/State tbf/state-w tbf/state-θ
    )
 
   (: apply-tbf-to-state (-> TBF (State (U Zero One)) (U Zero One)))
@@ -26,6 +28,14 @@
       (define st (hash 'x1 0 'x2 1))
       (define f (tbf #(1 1) 1))
       (check-equal? (apply-tbf-to-state f st) 0)))
+
+  (struct tbf/state ([weights : (VariableMapping Real)]
+                     [threshold : Real])
+    #:transparent
+    #:type-name TBF/State)
+  (define tbf/state-w tbf/state-weights)
+  (define tbf/state-θ tbf/state-threshold)
+
   )
 
 (module+ test