diff --git a/functions.rkt b/functions.rkt
index 97dcdeb..56f3110 100644
--- a/functions.rkt
+++ b/functions.rkt
@@ -28,7 +28,7 @@
  enumerate-boolean-functions/pv enumerate-boolean-functions/list
  random-boolean-table random-boolean-function random-boolean-function/list
 
- (struct-out tbf) tbf-w tbf-θ boolean->01/vector apply-tbf apply-tbf/boolean
+ (struct-out tbf) TBF tbf-w tbf-θ boolean->01/vector apply-tbf apply-tbf/boolean
  list->tbf lists->tbfs read-org-tbfs tbf-tabulate* tbf-tabulate
  tbf-tabulate*/boolean sbf? sbf list->sbf read-org-sbfs)
 
@@ -434,7 +434,8 @@
     (check-false (random-bool-f/list '(#t #f)))
     (check-true (random-bool-f/list '(#t #t)))))
 
-(struct tbf ([weights : (Vectorof Real)] [threshold : Real]) #:transparent)
+(struct tbf ([weights : (Vectorof Real)] [threshold : Real])
+  #:transparent #:type-name TBF)
 (define tbf-w tbf-weights)
 (define tbf-θ tbf-threshold)
 
@@ -446,7 +447,7 @@
   (test-case "boolean->01/vector"
     (check-equal? (boolean->01/vector #(#t #f #f)) #(1 0 0))))
 
-(: apply-tbf (-> tbf (Vectorof (U Zero One)) (U Zero One)))
+(: apply-tbf (-> TBF (Vectorof (U Zero One)) (U Zero One)))
 (define (apply-tbf tbf inputs)
   (any->01
    (>
@@ -462,7 +463,7 @@
     (check-equal? (tabulate/pv/01 2 (pvλ (x y) (apply-tbf f1 (vector x y))))
                   '((0 0 0) (0 1 0) (1 0 1) (1 1 0)))))
 
-(: apply-tbf/boolean (-> tbf (Vectorof Boolean) Boolean))
+(: apply-tbf/boolean (-> TBF (Vectorof Boolean) Boolean))
 (define (apply-tbf/boolean tbf inputs)
   (01->boolean (apply-tbf tbf (boolean->01/vector inputs))))
 
@@ -472,7 +473,7 @@
     (check-equal? (tabulate/pv/boolean 2 (pvλ (x y) (apply-tbf/boolean f1 (vector x y))))
                   '((#f #f #f) (#f #t #f) (#t #f #t) (#t #t #f)))))
 
-(: list->tbf (-> (Listof Real) tbf))
+(: list->tbf (-> (Listof Real) TBF))
 (define (list->tbf lst)
   (define-values (w θ) (split-at-right lst 1))
   (tbf (list->vector w) (car θ)))
@@ -481,7 +482,7 @@
   (test-case "list->tbf"
     (check-equal? (list->tbf '(1 2 3)) (tbf #(1 2) 3))))
 
-(: lists->tbfs (-> (Listof (Listof Real)) (Listof tbf)))
+(: lists->tbfs (-> (Listof (Listof Real)) (Listof TBF)))
 (define (lists->tbfs lsts)
   (map list->tbf lsts))
 
@@ -490,7 +491,7 @@
     (check-equal? (lists->tbfs '((1 2 3) (2 3 4)))
                   (list (tbf '#(1 2) 3) (tbf '#(2 3) 4)))))
 
-(: read-org-tbfs (->* (String) (#:headers Boolean) (Listof tbf)))
+(: read-org-tbfs (->* (String) (#:headers Boolean) (Listof TBF)))
 (define (read-org-tbfs str #:headers [headers #f])
   (define sexp (assert-type (read-org-sexp str) (Listof Any)))
   (define sexp-clean (cond [headers (cdr sexp)] [else sexp]))
@@ -501,7 +502,7 @@
     (check-equal? (read-org-tbfs "((1 2 1) (1 0 1))")
                   (list (tbf '#(1 2) 1) (tbf '#(1 0) 1)))))
 
-(: tbf-tabulate* (-> (Listof tbf) (Listof (Listof (U Zero One)))))
+(: tbf-tabulate* (-> (Listof TBF) (Listof (Listof (U Zero One)))))
 (define (tbf-tabulate* tbfs)
   (define funcs (for/list ([tbf tbfs])
                   : (Listof (-> (Listof (U Zero One)) (U Zero One)))
@@ -515,7 +516,7 @@
     (check-equal? (tbf-tabulate* (list (tbf #(2 2) 1) (tbf #(1 1) 1)))
                   '((0 0 0 0) (0 1 1 0) (1 0 1 0) (1 1 1 1)))))
 
-(: tbf-tabulate (-> tbf (Listof (Listof (U Zero One)))))
+(: tbf-tabulate (-> TBF (Listof (Listof (U Zero One)))))
 (define (tbf-tabulate t)
   (tbf-tabulate* (list t)))
 
@@ -524,7 +525,7 @@
     (check-equal? (tbf-tabulate (tbf #(1 2) 1))
                   '((0 0 0) (0 1 1) (1 0 0) (1 1 1)))))
 
-(: tbf-tabulate*/boolean (-> (Listof tbf) (Listof (Listof Boolean))))
+(: tbf-tabulate*/boolean (-> (Listof TBF) (Listof (Listof Boolean))))
 (define (tbf-tabulate*/boolean tbfs)
   (define funcs (for/list ([tbf tbfs])
                   : (Listof (-> (Listof Boolean) Boolean))
@@ -538,7 +539,7 @@
     (check-equal? (tbf-tabulate*/boolean (list (tbf #(1 2) 1)))
                   '((#f #f #f) (#f #t #t) (#t #f #f) (#t #t #t)))))
 
-(: sbf? (-> tbf Boolean))
+(: sbf? (-> TBF Boolean))
 (define (sbf? t)
   (= 0 (tbf-θ t)))
 
@@ -547,7 +548,7 @@
     (check-false (sbf? (tbf #(1 2) 3)))
     (check-true (sbf? (tbf #(1 2) 0)))))
 
-(: sbf (-> (Vectorof Real) tbf))
+(: sbf (-> (Vectorof Real) TBF))
 (define (sbf w)
   (tbf w 0))
 
@@ -555,14 +556,14 @@
   (test-case "sbf"
     (check-equal? (sbf #(1 -1)) (tbf '#(1 -1) 0))))
 
-(: list->sbf (-> (Listof Real) tbf))
+(: list->sbf (-> (Listof Real) TBF))
 (define (list->sbf lst) (sbf (list->vector lst)))
 
 (module+ test
   (test-case "list->sbf"
     (check-equal? (list->sbf '(1 -1)) (tbf '#(1 -1) 0))))
 
-(: read-org-sbfs (->* (String) (#:headers Boolean) (Listof tbf)))
+(: read-org-sbfs (->* (String) (#:headers Boolean) (Listof TBF)))
 (define (read-org-sbfs str #:headers [headers #f])
   (define sexp (assert-type (read-org-sexp str) (Listof Any)))
   (define sexp-clean (cond [headers (cdr sexp)] [else sexp]))
diff --git a/scribblings/functions.scrbl b/scribblings/functions.scrbl
index 84690aa..2478ac8 100644
--- a/scribblings/functions.scrbl
+++ b/scribblings/functions.scrbl
@@ -453,10 +453,20 @@ a list of arguments.
 A threshold Boolean function (TBF) is a pair @tt{(w, θ)}, where @tt{w} is
 a vector of weights and @tt{θ} is the threshold.
 
+Instances of @racket[tbf] have the type @racket[TBF].
+
 }
 
-@deftogether[(@defproc[(tbf-w [t tbf]) (Vectorof Real)]
-              @defproc[(tbf-θ [t tbf]) Real])]{
+@defidform[TBF]{
+
+The type of the instances of @racket[tbf]:
+
+@ex[
+(tbf #(1 2) 3)
+]}
+
+@deftogether[(@defproc[(tbf-w [t TBF]) (Vectorof Real)]
+              @defproc[(tbf-θ [t TBF]) Real])]{
 
 Shortcuts for @racket[tbf-weights] and @racket[tbf-threshold].
 
@@ -471,7 +481,7 @@ Converts a Boolean vector to a vector of zeros and ones.
 (boolean->01/vector #(#t #f #f))
 ]}
 
-@defproc[(apply-tbf [t tbf] [inputs (Vectorof (U Zero One))]) (U Zero One)]{
+@defproc[(apply-tbf [t TBF] [inputs (Vectorof (U Zero One))]) (U Zero One)]{
 
 Applies the TBF to its inputs.
 
@@ -484,7 +494,7 @@ above the threshold, the function is 1, otherwise it is 0.
 (tabulate/pv/01 2 (pvλ (x y) (apply-tbf simple-tbf (vector x y))))
 ]}
 
-@defproc[(apply-tbf/boolean [t tbf] [inputs (Vectorof Boolean)]) Boolean]{
+@defproc[(apply-tbf/boolean [t TBF] [inputs (Vectorof Boolean)]) Boolean]{
 
 Like @racket[apply-tbf], but takes Boolean values as inputs and outputs
 a Boolean value.
@@ -494,7 +504,7 @@ a Boolean value.
 (tabulate/pv/boolean 2 (pvλ (x y) (apply-tbf/boolean simple-tbf (vector x y))))
 ]}
 
-@defproc[(list->tbf [lst (Listof Real)]) tbf]{
+@defproc[(list->tbf [lst (Listof Real)]) TBF]{
 
 Converts a list of numbers to a TBF.  The last element of the list is taken to
 be the threshold, while the other elements are taken to be the weights.
@@ -503,7 +513,7 @@ be the threshold, while the other elements are taken to be the weights.
 (list->tbf '(1 2 3))
 ]}
 
-@defproc[(lists->tbfs [lsts (Listof (Listof Real))]) (Listof tbf)]{
+@defproc[(lists->tbfs [lsts (Listof (Listof Real))]) (Listof TBF)]{
 
 Converts multiple lists of numbers to a list of TBFs.
 
@@ -515,7 +525,7 @@ The main use is for reading TBFs from Org-mode tables read by
 ]}
 
 @defproc[(read-org-tbfs [str String] [#:headers headers Boolean #f])
-			(Listof tbf)]{
+			(Listof TBF)]{
 
 Reads a list of TBF from an Org-mode string containing a sexp, containing
 a list of lists of numbers.  If headers is @racket[#t], drops the first list,
@@ -528,7 +538,7 @@ The input is typically what @racket[read-org-sexp] reads.
 (read-org-tbfs "((x y f) (1 2 1) (1 0 1))" #:headers #t)
 ]}
 
-@defproc[(tbf-tabulate* [tbfs (Listof tbf)])
+@defproc[(tbf-tabulate* [tbfs (Listof TBF)])
 			(Listof (Listof (U Zero One)))]{
 
 Tabulates a list of TBFs.
@@ -544,7 +554,7 @@ TBF in the list.
 (tbf-tabulate* (list (tbf #(2 2) 1) (tbf #(1 1) 1)))
 ]}
 
-@defproc[(tbf-tabulate [t tbf])
+@defproc[(tbf-tabulate [t TBF])
 		       (Listof (Listof (U Zero One)))]{
 
 Tabulates a single TBF.
@@ -553,7 +563,7 @@ Tabulates a single TBF.
 (tbf-tabulate (tbf #(1 2) 1))
 ]}
 
-@defproc[(tbf-tabulate*/boolean [tbfs (Listof tbf)])
+@defproc[(tbf-tabulate*/boolean [tbfs (Listof TBF)])
 				(Listof (Listof Boolean))]{
 
 Tabulates a list of TBFs like @racket[tbf-tabulate*], but uses Boolean values
@@ -566,7 +576,7 @@ TBF in the list.
 (tbf-tabulate*/boolean (list (tbf #(1 2) 1)))
 ]}
 
-@defproc[(sbf? [t tbf]) Boolean]{
+@defproc[(sbf? [t TBF]) Boolean]{
 
 A sign Boolean function (SBF) is a TBF whose threshold is 0.
 
@@ -575,7 +585,7 @@ A sign Boolean function (SBF) is a TBF whose threshold is 0.
 (sbf? (tbf #(1 2) 0))
 ]}
 
-@defproc[(sbf [w (Vectorof Real)]) tbf]{
+@defproc[(sbf [w (Vectorof Real)]) TBF]{
 
 Creates a TBF which is an SBF from a vector of weights.
 
@@ -584,7 +594,7 @@ Creates a TBF which is an SBF from a vector of weights.
 ]}
 
 @defproc[(list->sbf [lst (Listof Real)])
-		    tbf]{
+		    TBF]{
 
 Converts a list of numbers to an SBF.  The elements of the list are taken to be
 the weights of the SBF.
@@ -594,7 +604,7 @@ the weights of the SBF.
 ]}
 
 @defproc[(read-org-sbfs [str String] [#:headers headers Boolean #f])
-			(Listof tbf)]{
+			(Listof TBF)]{
 
 Reads a list of SBF from an Org-mode string containing a sexp, containing
 a list of lists of numbers.  If headers is @racket[#t], drops the first list,