diff --git a/functions.rkt b/functions.rkt
index edbd2f1..e13f179 100644
--- a/functions.rkt
+++ b/functions.rkt
@@ -155,7 +155,7 @@
       (check-equal? (tabulate/pv (pvλ (x y) (and x y)) '((#f #t) (#f #t)))
                     '((#f #f #f) (#f #t #f) (#t #f #f) (#t #t #t)))))
 
-  (: tabulate/pv/boolean (-> Integer (-> Boolean * Boolean) (Listof (Listof Boolean))))
+  (: tabulate/pv/boolean (-> Positive-Integer (-> Boolean * Boolean) (Listof (Listof Boolean))))
   (define (tabulate/pv/boolean arity func)
     (tabulate/pv func (make-list arity '(#f #t))))
 
@@ -164,7 +164,7 @@
       (check-equal? (tabulate/pv/boolean 2 (pvλ (x y) (and x y)))
                     '((#f #f #f) (#f #t #f) (#t #f #f) (#t #t #t)))))
 
-  (: tabulate*/pv/boolean (-> Integer (Listof (-> Boolean * Boolean))
+  (: tabulate*/pv/boolean (-> Positive-Integer (Listof (-> Boolean * Boolean))
                               (Listof (Listof Boolean))))
   (define (tabulate*/pv/boolean arity funcs)
     (tabulate*/pv funcs (make-list arity '(#f #t))))
@@ -175,7 +175,7 @@
                                                   (pvλ (x y) (or x y))))
                     '((#f #f #f #f) (#f #t #f #t) (#t #f #f #t) (#t #t #t #t)))))
 
-  (: tabulate/pv/01 (-> Integer (-> (U Zero One) * (U Zero One))
+  (: tabulate/pv/01 (-> Positive-Integer (-> (U Zero One) * (U Zero One))
                         (Listof (Listof (U Zero One)))))
   (define (tabulate/pv/01 arity func)
     (tabulate/pv func (make-list arity '(0 1))))
@@ -186,7 +186,7 @@
                                            (cast (modulo (+ x y) 2) (U Zero One))))
                     '((0 0 0) (0 1 1) (1 0 1) (1 1 0)))))
 
-  (: tabulate*/pv/01 (-> Integer (Listof (-> (U Zero One) * (U Zero One)))
+  (: tabulate*/pv/01 (-> Positive-Integer (Listof (-> (U Zero One) * (U Zero One)))
                          (Listof (Listof (U Zero One)))))
   (define (tabulate*/pv/01 arity funcs)
     (tabulate*/pv funcs (make-list arity '(0 1))))
@@ -241,7 +241,7 @@
       (check-false (negation #t))
       (check-exn exn:fail? (λ () (negation #f #t)))))
 
-  (: enumerate-boolean-tables (-> Integer (Sequenceof (Listof (Listof Boolean)))))
+  (: enumerate-boolean-tables (-> Positive-Integer (Sequenceof (Listof (Listof Boolean)))))
   (define (enumerate-boolean-tables n)
     (define inputs (boolean-power n))
     (define outputs (boolean-power/stream (cast (expt 2 n) Integer)))
@@ -280,7 +280,7 @@
                       ((#f #f #t) (#f #t #t) (#t #f #t) (#t #t #f))
                       ((#f #f #t) (#f #t #t) (#t #f #t) (#t #t #t))))))
 
-  (: enumerate-boolean-functions (-> Integer (Sequenceof (-> Boolean * Boolean))))
+  (: enumerate-boolean-functions (-> Positive-Integer (Sequenceof (-> Boolean * Boolean))))
   (define (enumerate-boolean-functions n)
     (stream-map (inst table->function Boolean) (enumerate-boolean-tables n)))
 
@@ -290,7 +290,7 @@
       (check-false (bool-f1 #f))
       (check-false (bool-f1 #t))))
 
-  (: enumerate-boolean-functions/pv (-> Integer (Sequenceof (-> Boolean * Boolean))))
+  (: enumerate-boolean-functions/pv (-> Positive-Integer (Sequenceof (-> Boolean * Boolean))))
   (define (enumerate-boolean-functions/pv n)
     (stream-map (inst table->function/pv Boolean) (enumerate-boolean-tables n)))
 
@@ -302,7 +302,7 @@
       (check-exn exn:fail? (λ () (bool-f1/pv #f #f)))))
 
   (: enumerate-boolean-functions/list
-     (-> Integer (Sequenceof (-> (Listof Boolean) Boolean))))
+     (-> Positive-Integer (Sequenceof (-> (Listof Boolean) Boolean))))
   (define (enumerate-boolean-functions/list n)
     (stream-map (inst table->function/list Boolean) (enumerate-boolean-tables n)))
 
@@ -312,7 +312,7 @@
       (check-false (bool-f1/list '(#f)))
       (check-false (bool-f1/list '(#t)))))
 
-  (: random-boolean-table (-> Integer (Listof (Listof Boolean))))
+  (: random-boolean-table (-> Positive-Integer (Listof (Listof Boolean))))
   (define (random-boolean-table n)
     (define ins (boolean-power n))
     (define outs (stream-take (in-random 2) (cast (expt 2 n) Nonnegative-Integer)))
@@ -328,7 +328,7 @@
                       (#t #f #f)
                       (#t #t #t)))))
 
-  (: random-boolean-function (-> Integer (-> Boolean * Boolean)))
+  (: random-boolean-function (-> Positive-Integer (-> Boolean * Boolean)))
   (define (random-boolean-function n)
     (table->function (random-boolean-table n)))
 
diff --git a/scribblings/functions.scrbl b/scribblings/functions.scrbl
index dcd924c..8121393 100644
--- a/scribblings/functions.scrbl
+++ b/scribblings/functions.scrbl
@@ -167,7 +167,7 @@ are @seclink["pseudovariadic"]{pseudovariadic}.
               '((#f #t) (#f #t)))
 ]}
 
-@defproc[(tabulate/pv/boolean [arity Integer] [func (-> Boolean * Boolean)])
+@defproc[(tabulate/pv/boolean [arity Positive-Integer] [func (-> Boolean * Boolean)])
 			      (Listof (Listof Boolean))]{
 
 Like @racket[tabulate/pv], but assumes the domains of all variables of the
@@ -198,7 +198,7 @@ this function.
 
 }
 
-@defproc[(tabulate*/pv/boolean [arity Integer]
+@defproc[(tabulate*/pv/boolean [arity Positive-Integer]
 			       [func (Listof (-> Boolean * Boolean))])
 			       (Listof (Listof Boolean))]{
 
@@ -210,7 +210,7 @@ same arity.
                               (pvλ (x y) (or x y))))
 ]}
 
-@defproc[(tabulate/pv/01 [arity Integer] [func (-> (U Zero One) * (U Zero One))])
+@defproc[(tabulate/pv/01 [arity Positive-Integer] [func (-> (U Zero One) * (U Zero One))])
 			 (Listof (Listof (U Zero One)))]{
 
 Like @racket[tabulate/pv], but assumes the domains of all variables of the
@@ -228,7 +228,7 @@ See @racket[tabulate/pv/boolean] for an explanation of the explicit
 
 }
 
-@defproc[(tabulate*/pv/01 [arity Integer]
+@defproc[(tabulate*/pv/01 [arity Positive-Integer]
 			  [func (Listof (-> (U Zero One) * (U Zero One)))])
 			  (Listof (Listof (U Zero One)))]{
 
@@ -290,7 +290,7 @@ the returned by @racket[table->function/pv] is
 (eval:error (my-and #f))
 ]}
 
-@defproc[(enumerate-boolean-tables [n Integer])
+@defproc[(enumerate-boolean-tables [n Positive-Integer])
 				    (Sequenceof (Listof (Listof Boolean)))]{
 
 Returns the stream of the truth tables of all Boolean functions of
@@ -303,7 +303,7 @@ There are @tt{2^(2^n)} Boolean functions of arity @racket[n].
 (stream->list (enumerate-boolean-tables 1))
 ]}
 
-@defproc[(enumerate-boolean-functions [n Integer])
+@defproc[(enumerate-boolean-functions [n Positive-Integer])
 				      (Sequenceof (-> Boolean * Boolean))]{
 
 Returns the stream of all Boolean functions of a given arity @racket[n].
@@ -314,7 +314,7 @@ There are @tt{2^(2^n)} Boolean functions of arity @racket[n].
 (length (stream->list (enumerate-boolean-functions 2)))
 ]}
 
-@defproc[(enumerate-boolean-functions/pv [n Integer])
+@defproc[(enumerate-boolean-functions/pv [n Positive-Integer])
 					 (Sequenceof (-> Boolean * Boolean))]{
 
 Like @racket[enumerate-boolean-functions], but the returned functions are
@@ -327,7 +327,7 @@ Like @racket[enumerate-boolean-functions], but the returned functions are
 ]}
 
 @defproc[(enumerate-boolean-functions/list
-	  [n Integer])
+	  [n Positive-Integer])
 	  (Sequenceof (-> (Listof Boolean) Boolean))]{
 
 Like @racket[enumerate-boolean-functions], but the returned functions take
@@ -340,7 +340,7 @@ their arguments as a single list.
 
 @section{Random functions}
 
-@defproc[(random-boolean-table [n Integer]) (Listof (Listof Boolean))]{
+@defproc[(random-boolean-table [n Positive-Integer]) (Listof (Listof Boolean))]{
 
 Generates a random truth table for a Boolean function of arity @racket[n].
 
@@ -348,7 +348,7 @@ Generates a random truth table for a Boolean function of arity @racket[n].
 (random-boolean-table 2)
 ]}
 
-@defproc[(random-boolean-function [n Integer]) (-> Boolean * Boolean)]{
+@defproc[(random-boolean-function [n Positive-Integer]) (-> Boolean * Boolean)]{
 
 Generates a random Boolean function of arity @racket[n].