diff --git a/collects/math/private/bigfloat/bigfloat-mpfr.rkt b/collects/math/private/bigfloat/bigfloat-mpfr.rkt
index b859a81dd1..0ab57d4c48 100644
--- a/collects/math/private/bigfloat/bigfloat-mpfr.rkt
+++ b/collects/math/private/bigfloat/bigfloat-mpfr.rkt
@@ -137,6 +137,15 @@
   (define bits (bf-precision))
   (bf (random-bits bits) (- bits)))
 
+(: bigfloat->fl2 (Bigfloat -> (Values Flonum Flonum)))
+(define (bigfloat->fl2 x)
+  (define x2 (bigfloat->flonum x))
+  (values x2 (bigfloat->flonum (bf- x (flonum->bigfloat x2)))))
+
+(: fl2->bigfloat (Flonum Flonum -> Bigfloat))
+(define (fl2->bigfloat x2 x1)
+  (bf+ (flonum->bigfloat x1) (flonum->bigfloat x2)))
+
 (provide
  ;; Library stuffs
  mpfr-available?
@@ -159,10 +168,12 @@
  integer->bigfloat
  rational->bigfloat
  real->bigfloat
+ fl2->bigfloat
  bigfloat->flonum
  bigfloat->integer
  bigfloat->rational
  bigfloat->real
+ bigfloat->fl2
  ;; String conversion
  bigfloat->string
  string->bigfloat
diff --git a/collects/math/private/bigfloat/mpfr.rkt b/collects/math/private/bigfloat/mpfr.rkt
index 63098193bc..a7e158cf95 100644
--- a/collects/math/private/bigfloat/mpfr.rkt
+++ b/collects/math/private/bigfloat/mpfr.rkt
@@ -1001,24 +1001,6 @@
   (set! 0ary-funs (list* #'phi.bf #'epsilon.bf #'-max.bf #'-min.bf #'+min.bf #'+max.bf
                          0ary-funs)))
 
-;; ===================================================================================================
-;; Extra functions
-
-(define (random-bits bits)
-  (let loop ([bits bits] [acc 0])
-    (cond [(= 0 bits)  acc]
-          [else
-           (define new-bits (min 24 bits))
-           (loop (- bits new-bits)
-                 (bitwise-ior (random (arithmetic-shift 1 new-bits))
-                              (arithmetic-shift acc new-bits)))])))
-
-(define (bfrandom)
-  (define bits (bf-precision))
-  (bf (random-bits bits) (- bits)))
-
-(provide bfrandom)
-
 ;; ===================================================================================================
 ;; Number Theoretic Functions
 ;; http://gmplib.org/manual/Number-Theoretic-Functions.html#Number-Theoretic-Functions
diff --git a/collects/math/private/flonum/expansion/expansion-base.rkt b/collects/math/private/flonum/expansion/expansion-base.rkt
index f12ba2355e..7c0a244aab 100644
--- a/collects/math/private/flonum/expansion/expansion-base.rkt
+++ b/collects/math/private/flonum/expansion/expansion-base.rkt
@@ -9,10 +9,9 @@ Discrete & Computational Geometry 18(3):305–363, October 1997
 |#
 
 (require "../flonum-functions.rkt"
-         "../flonum-syntax.rkt"
-         "../../bigfloat/bigfloat-struct.rkt")
+         "../flonum-syntax.rkt")
 
-(provide fl2 bigfloat->fl2 fl2->real fl2->bigfloat
+(provide fl2 fl2->real
          fl2+ fl2- fl2*split-fl fl2* fl2/
          flsqrt/error fl2sqrt)
 
@@ -31,11 +30,6 @@ Discrete & Computational Geometry 18(3):305–363, October 1997
     [(x y)
      (fast-fl+/error x y)]))
 
-(: bigfloat->fl2 (Bigfloat -> (Values Flonum Flonum)))
-(define (bigfloat->fl2 x)
-  (define x2 (bigfloat->flonum x))
-  (values x2 (bigfloat->flonum (bf- x (bf x2)))))
-
 (: fl2->real (Flonum Flonum -> Real))
 (define (fl2->real x2 x1)
   (cond [(and (x1 . fl> . -inf.0) (x1 . fl< . +inf.0)
@@ -43,10 +37,6 @@ Discrete & Computational Geometry 18(3):305–363, October 1997
          (+ (inexact->exact x2) (inexact->exact x1))]
         [else  (fl+ x1 x2)]))
 
-(: fl2->bigfloat (Flonum Flonum -> Bigfloat))
-(define (fl2->bigfloat x2 x1)
-  (bf+ (bf x1) (bf x2)))
-
 (: fl3->fl2 (Flonum Flonum Flonum -> (Values Flonum Flonum)))
 (define (fl3->fl2 e3 e2 e1)
   (values e3 (fl+ e2 e1)))
diff --git a/collects/math/private/number-theory/divisibility.rkt b/collects/math/private/number-theory/divisibility.rkt
index d9c3706312..bb57c1764a 100644
--- a/collects/math/private/number-theory/divisibility.rkt
+++ b/collects/math/private/number-theory/divisibility.rkt
@@ -7,9 +7,10 @@
 ;;;
 
 (: divides? : Integer Integer -> Boolean)
-; For b<>0:  ( a divides b <=> exists k s.t. a*k=b )
+; a divides b <=> exists unique k s.t. a*k=b
 (define (divides? a b)
-  (= (remainder b a) 0))
+  (cond [(zero? a)  #f]
+        [else  (= (remainder b a) 0)]))
 
 ; DEF (Coprime, relatively prime)
 ;  Two or more integers are called coprime, if their greatest common divisor is 1.
diff --git a/collects/math/private/number-theory/modular-arithmetic-base.rkt b/collects/math/private/number-theory/modular-arithmetic-base.rkt
index 4af133b111..182945606b 100644
--- a/collects/math/private/number-theory/modular-arithmetic-base.rkt
+++ b/collects/math/private/number-theory/modular-arithmetic-base.rkt
@@ -23,8 +23,12 @@
   
   (provide (all-defined-out))
   
-  (: current-modulus-param (Parameterof Positive-Integer))
-  (define current-modulus-param (make-parameter 1))
+  (: current-modulus-param (Parameterof Integer Positive-Integer))
+  (define current-modulus-param
+    (make-parameter
+     1 (λ: ([n : Integer])
+         (cond [(n . <= . 0)  (raise-argument-error 'with-modulus "Positive-Integer" n)]
+               [else  n]))))
   
   (: current-modulus (-> Positive-Integer))
   (begin-encourage-inline
diff --git a/collects/math/private/number-theory/number-theory.rkt b/collects/math/private/number-theory/number-theory.rkt
index 4ff2ccfa7e..8b1d6864fb 100644
--- a/collects/math/private/number-theory/number-theory.rkt
+++ b/collects/math/private/number-theory/number-theory.rkt
@@ -107,8 +107,10 @@
 
 ; Example : (solve-chinese '(2 3 2) '(3 5 7)) = 23
 
-(: solve-chinese : Zs (Listof N+) -> N)
+(: solve-chinese : Zs (Listof Z) -> N)
 (define (solve-chinese as ns)
+  (unless (andmap positive? ns)
+    (raise-argument-error 'solve-chinese "(Listof Positive-Integer)" 1 as ns))
   ; the ns should be coprime
   (let* ([n  (apply * ns)]
          [cs (map (λ: ([ni : Z]) (quotient n ni)) ns)]
@@ -245,35 +247,43 @@
                      (prev-prime n-2)))]))
 
 
-(: next-primes : Z N -> Zs)
+(: next-primes : Z Z -> Zs)
 (define (next-primes m primes-wanted)
-  (: loop : Z Z -> Zs)
-  (define (loop n primes-wanted)
-    (if (= primes-wanted 0)
-        '()
-        (let ([next (next-prime n)])
-          (if next
-              (cons next (loop next (sub1 primes-wanted)))
-              '()))))
-  (loop m primes-wanted))
+  (cond
+    [(primes-wanted . < . 0)  (raise-argument-error 'next-primes "Natural" 1 m primes-wanted)]
+    [else
+     (: loop : Z Z -> Zs)
+     (define (loop n primes-wanted)
+       (if (= primes-wanted 0)
+           '()
+           (let ([next (next-prime n)])
+             (if next
+                 (cons next (loop next (sub1 primes-wanted)))
+                 '()))))
+     (loop m primes-wanted)]))
 
-(: prev-primes : Z N -> Zs)
+(: prev-primes : Z Z -> Zs)
 (define (prev-primes m primes-wanted)
-  (: loop : Z Z -> Zs)
-  (define (loop n primes-wanted)
-    (if (= primes-wanted 0)
-        '()
-        (let ([prev (prev-prime n)])
-          (if prev
-              (cons prev (loop prev (sub1 primes-wanted)))
-              '()))))
-  (loop m primes-wanted))
+  (cond
+    [(primes-wanted . < . 0)  (raise-argument-error 'prev-primes "Natural" 1 m primes-wanted)]
+    [else
+     (: loop : Z Z -> Zs)
+     (define (loop n primes-wanted)
+       (if (= primes-wanted 0)
+           '()
+           (let ([prev (prev-prime n)])
+             (if prev
+                 (cons prev (loop prev (sub1 primes-wanted)))
+                 '()))))
+     (loop m primes-wanted)]))
 
 
-(: nth-prime : N -> Prime)
+(: nth-prime : Z -> Prime)
 (define (nth-prime n)
-  (for/fold: ([p : Prime  2]) ([m (in-range n)])
-    (next-prime p)))
+  (cond [(n . < . 0)  (raise-argument-error 'nth-prime "Natural" n)]
+        [else
+         (for/fold: ([p : Prime  2]) ([m (in-range n)])
+           (next-prime p))]))
 
 
 ;;;
diff --git a/collects/math/private/number-theory/quadratic-residues.rkt b/collects/math/private/number-theory/quadratic-residues.rkt
index 1d8bc5244b..06eab941f3 100644
--- a/collects/math/private/number-theory/quadratic-residues.rkt
+++ b/collects/math/private/number-theory/quadratic-residues.rkt
@@ -13,12 +13,13 @@
 ;   The number s is called a squre root of a modulo n.
 
 ; p is prime
-(: quadratic-character : Integer Integer -> Integer)
+(: quadratic-character : Integer Integer -> (U -1 0 1))
 (define (quadratic-character a p)
   (cond [(a . < . 0)  (raise-argument-error 'quadratic-character "Natural" 0 a p)]
         [(p . <= . 0)  (raise-argument-error 'quadratic-character "Positive-Integer" 1 a p)]
         [else  (let ([l  (modular-expt a (quotient (- p 1) 2) p)])
-                 (if (<= 0 l 1) l -1))]))
+                 (cond [(or (eqv? l 0) (eqv? l 1))  l]
+                       [else  -1]))]))
 
 (: quadratic-residue? : Integer Integer -> Boolean)
 (define (quadratic-residue? a n)
diff --git a/collects/math/scribblings/math-number-theory.scrbl b/collects/math/scribblings/math-number-theory.scrbl
index 18356df8aa..aab9e239db 100644
--- a/collects/math/scribblings/math-number-theory.scrbl
+++ b/collects/math/scribblings/math-number-theory.scrbl
@@ -1,8 +1,12 @@
-#lang scribble/doc
+#lang scribble/manual
 @(require (for-label racket/flonum
                      racket/fixnum
                      racket/unsafe/ops
                      racket/require
+                     racket/base
+                     (only-in typed/racket/base
+                              Integer Exact-Rational Boolean Listof Natural U List
+                              Positive-Integer)
                      math)
           scribble/extract
           scribble/eval
@@ -13,107 +17,88 @@
           "utils.rkt")
 
 @(define untyped-eval (make-untyped-math-eval))
+@interaction-eval[#:eval untyped-eval (require racket/list
+                                               racket/function)]
 
 @(define math-style tt)
 
-@(define math-eval 
-   (parameterize ([sandbox-output 'string]
-                  [sandbox-error-output 'string])
-     (make-evaluator 'racket)))
-@;(interaction-eval #:eval math-eval (require racket math))
-
-
-@title[#:tag "number-theory" #:style '(toc)]{Number Theory}
+@title[#:tag "number-theory"]{Number Theory}
 @(author-jens-axel)
 
+@defmodule[math/number-theory]
+
 @local-table-of-contents[]
 
 @; ----------------------------------------
 @section[#:tag "congruences"]{Congruences and Modular Arithmetic}
 
 @margin-note{Wikipedia: @hyperlink["http://en.wikipedia.org/wiki/Divisor"]{Divisor}}
-@defproc[(divides? [m Integer] [n Integer]) boolean?]{
-   Returns @racket[#t] if @racket[m] divides @racket[n],
-   @racket[#f] otherwise.
+@defproc[(divides? [m Integer] [n Integer]) Boolean]{
+   Returns @racket[#t] if @racket[m] divides @racket[n], @racket[#f] otherwise.
+           
+   Formally, an integer @racket[m] divides an integer @racket[n] when there
+   exists a unique integer @racket[k] such that @racket[(* m k) = n].
 
-   Note: That a non-zero integer @racket[m] divides an integer @racket[n]
-   means there exists an integer @racket[k] such that m*k=n.
-
-   Test whether 2 divides 9:
+   @examples[#:eval untyped-eval
+                    (divides? 2 9)
+                    (divides? 2 8)]
+   
+   Note that @racket[0] cannot divide anything:
    @interaction[#:eval untyped-eval
-                       (require math)
-                       (divides? 2 9)]   
-}   
+                       (divides? 0 5)
+                       (divides? 0 0)]
+   
+   Practically, if @racket[(divides? m n)] is @racket[#t], then @racket[(/ n m)] will return
+   an integer and will not raise @racket[exn:fail:contract:divide-by-zero].
+   
+}
 
 @margin-note{Wikipedia: @hyperlink["http://en.wikipedia.org/wiki/B%C3%A9zout's_identity"]{Bezout's Identity}}
 @defproc[(bezout [a Integer] [b Integer] [c Integer] ...) (Listof Integer)]{
-  Given integers @racket[a], @racket[b], @racket[c] ... 
-  returns a list of integers @racket[u], @racket[v], @racket[q] ... 
-  such that @racket[gcd](@racket[a],@racket[b],@racket[c],...) 
-  = @racket[au + bv + cw + ...]
+  Given integers @racket[a b c ...] returns a list of integers @racket[(list u v w ...)]
+  such that @racket[(gcd a b c ...) = (+ (* a u) (* b v) (* c w) ...)].
 
-  The greatest common divisor of 6 and 15 is 3.
-  @interaction[#:eval untyped-eval
-                      (bezout 6 15)
-                      (+ (* -2 6) (* 1 15))]
+  @examples[#:eval untyped-eval
+                   (bezout 6 15)
+                   (+ (* -2 6) (* 1 15))
+                   (gcd 6 15)]
 }
-  
-@margin-note{Wikipedia: @hyperlink["http://en.wikipedia.org/wiki/Coprime"]{Coprime}}
-@defproc[(coprime? [a Integer] [b Integer] ...) boolean?]{
-  Returns @racket[#t] if the integers @racket[a],@racket[b],... are coprime.
 
-  Note: A set of integers are considered coprime (also called relatively prime)
+@margin-note{Wikipedia: @hyperlink["http://en.wikipedia.org/wiki/Coprime"]{Coprime}}
+@defproc[(coprime? [a Integer] [b Integer] ...) Boolean]{
+  Returns @racket[#t] if the integers @racket[a b ...] are coprime.
+  Formally, a set of integers is considered coprime (also called relatively prime)
   if their greatest common divisor is 1.
 
-  The numbers 2, 6, and, 15 are coprime.
-  @interaction[#:eval untyped-eval
-                      (coprime? 2 6 15)]
-}  
-
+  @examples[#:eval untyped-eval
+                   (coprime? 2 6 15)]
+}
  
 @margin-note{Wikipedia: @hyperlink["http://en.wikipedia.org/wiki/Pairwise_coprime"]{Pairwise Coprime}}
-@defproc[(pairwise-coprime? [a Integer] [b Integer] ...) boolean?]{
-  Returns @racket[#t] if the integers @racket[a],@racket[b],... are pairwise coprime.
+@defproc[(pairwise-coprime? [a Integer] [b Integer] ...) Boolean]{
+  Returns @racket[#t] if the integers @racket[a b ...] are @italic{pairwise} coprime, meaning
+  that each adjacent pair of integers is coprime.
 
-  The numbers 2, 6, and, 15 are not pairwise coprime, since 2 and 6 share the factor 3.
-  @interaction[#:eval untyped-eval
-                      (pairwise-coprime? 2 6 15)]
-}  
+The numbers 2, 6 and 15 are coprime, but not @italic{pairwise} coprime, because 2 and 6 share the
+factor 3:
+@interaction[#:eval untyped-eval
+                    (pairwise-coprime? 2 6 15)]
+}
 
-@margin-note{Wikipedia: @hyperlink["http://en.wikipedia.org/wiki/Modular_multiplicative_inverse"]{Multiplicative Inverse}}
-@defproc[(modular-inverse [a Integer] [n Integer]) natural?]{
-  Returns the inverse of @racket[a] module @racket[n],
-  if @racket[a] and @racket[n] are coprime,
-  otherwise @racket[#f] is returned.
+@margin-note{Wikipedia: @hyperlink["http://en.wikipedia.org/wiki/Chinese_remainder_theorem"]{Chinese Remainder Theorem}}
+@defproc[(solve-chinese [as (Listof Integer)] [ns (Listof Integer)]) Natural]{
+  Given a length-@racket[k] list of integers @racket[as] and a length-@racket[k] list of coprime
+  moduli @racket[ns], @racket[(solve-chinese as ns)] returns the least natural number @racket[x]
+  that is a solution to the equations
+
+  @racketblock[x = #,(elem @racket[a] @subscript{1}) #,(elem "(mod " @racket[n] @subscript{1} ")")
+                ...
+               x = #,(elem @racket[a] @subscript{@racket[k]}) #,(elem "(mod " @racket[x] @subscript{@racket[k]} ")")]
+
+  The solution @racket[x] is less than
+  @racket[(* #,(elem @racket[n] @subscript{1}) ... #,(elem @racket[n] @subscript{@racket[k]}))].
   
-  Note: If @racket[a] and @racket[n] are coprime, then
-  the inverse, @racket[b], is a number in the set @racket[{0,...,n-1}]
-  such that @racket[ab=1 mod n].
-  
-  The number 3 is an inverse to 2 modulo 5.
-  @interaction[(require math)
-               (modular-inverse 2 5)
-               (modulo (* 2 3) 5)]
-  The number 0 has no inverse modulo 5.
-  @interaction[(require math)
-               (modular-inverse 0 5)]
-}  
-
-
-
-@defproc[(solve-chinese [as (Listof Integer)] [bs (Listof Integer)]) natural?]{
-  @margin-note{Wikipedia: @hyperlink["http://en.wikipedia.org/wiki/Chinese_remainder_theorem"]{Chinese Remainder Theorem}}
-  Given a list of integers @racket[as] and a list of coprime moduli @racket[ns]
-  the function @racket[solve-chinese] will return
-  the single natural solution @racket[x] in @racket[{0,...,n-1}]
-  to the equations
-
-  @racket[x=a1  mod n1,  ...,  x=ak  mod nk]
-
-  where @racket[a1], ... are the elements of @racket[as],  
-  and   @racket[n1], ... are the elements of @racket[ns],  
-  and   @racket[n=n1*...*nk].
-
+  The moduli @racket[ns] must all be positive.
   
   What is the least number @racket[x] that when divided by 3 leaves 
   a remainder of 2, when divided by 5 leaves a remainder of 3, and 
@@ -122,57 +107,187 @@
                       (solve-chinese '(2 3 2) '(3 5 7))]  
 }
 
-@defproc[(quadratic-residue? [a natural?] [n natural?]) boolean?]{
-Returns @racket[#t] if @racket[a] is a quadratic residue modulo @racket[n],        
-otherwise @racket[#f] is returned. 
+@defproc[(quadratic-residue? [a Integer] [n Integer]) Boolean]{
+Returns @racket[#t] if @racket[a] is a quadratic residue modulo @racket[n], otherwise @racket[#f].
+The modulus @racket[n] must be positive, and @racket[a] must be nonnegative.
 
-A number @racket[a] is a quadratic residue modulo @racket[n], if there
-exists a number @racket[x] such that @math-style{x^2=a mod n}.
-  @interaction[(require math)
-               (quadratic-residue? 0 4)
-               (quadratic-residue? 1 4)
-               (quadratic-residue? 2 4)
-               (quadratic-residue? 3 4)]
+Formally, @racket[a] is a quadratic residue modulo @racket[n] if there
+exists a number @racket[x] such that @racket[(* x x) = a] (mod @racket[n]).
+In other words, @racket[(quadratic-residue? a n)] is @racket[#t] when
+@racket[a] is a perfect square modulo @racket[n].
+
+@examples[#:eval untyped-eval
+                 (quadratic-residue? 0 4)
+                 (quadratic-residue? 1 4)
+                 (quadratic-residue? 2 4)
+                 (quadratic-residue? 3 4)]
 }
 
-@defproc[(quadratic-character [a natural?] [p prime?]) (union -1 1)]{
-Returns the values of the quadratic character modulo the prime @racket[p].                                                               
+@defproc[(quadratic-character [a Integer] [p Integer]) (U -1 0 1)]{
+Returns the value of the quadratic character modulo the prime @racket[p].                                                              
 That is, for a non-zero @racket[a] the number @racket[1] is returned when 
 @racket[a] is a quadratic residue,
 and @racket[-1] is returned when @racket[a] is a non-residue. 
 If @racket[a] is zero, then @racket[0] is returned.
-        
-This function is also known as the @emph{Legendre Symbol}.
 
-  @interaction[(require math)
-               (quadratic-character 0 4)
-               (quadratic-character 1 4)
-               (quadratic-character 2 4)
-               (quadratic-character 3 4)]
+If @racket[a] is negative or @racket[p] is not positive, @racket[quadratic-character] raises an error.
+If @racket[p] is not prime, @racket[(quadratic-character a p)] is indeterminate.
+        
+This function is also known as the @emph{Legendre symbol}.
+
+  @interaction[#:eval untyped-eval
+                      (quadratic-character 0 5)
+                      (quadratic-character 1 5)
+                      (quadratic-character 2 5)
+                      (quadratic-character 3 5)]
 }
 
+@margin-note{Wikipedia: @hyperlink["http://en.wikipedia.org/wiki/Modular_multiplicative_inverse"]{Multiplicative Inverse}}
+@defproc[(modular-inverse [a Integer] [n Integer]) Natural]{
+  Returns the inverse of @racket[a] modulo @racket[n] if @racket[a] and @racket[n] are coprime,
+  otherwise raises an error. The modulus @racket[n] must be positive, and @racket[a] must be nonzero.
+  
+  Formally, if @racket[a] and @racket[n] are coprime, @racket[b = (modular-inverse a n)] is the
+  unique natural number less than @racket[n] such that @racket[(* a b) = 1] (mod @racket[n]).
+  
+  @interaction[#:eval untyped-eval
+                      (modular-inverse 2 5)
+                      (modulo (* 2 3) 5)]
+}
+
+@defproc[(modular-expt [a Integer] [b Integer] [n Integer]) Natural]{
+  Computes @racket[(modulo (expt a b) n)], but much more efficiently. The modulus @racket[n] must
+  be positive, and the exponent @racket[b] must be nonnegative.
+  
+  @examples[#:eval untyped-eval
+                   (modulo (expt -6 523) 19)
+                   (modular-expt -6 523 19)
+                   (modular-expt 9 158235208 19)
+                   (eval:alts (code:line (code:comment "don't try this at home!")
+                                         (modulo (expt 9 158235208) 19))
+                              (eval:result @racketresultfont{4}))
+                   ]
+}
+
+@subsection[#:tag "modular"]{Parameterized Modular Arithmetic}
+
+The @racketmodname[math/number-theory] library supports modular arithmetic parameterized on a current
+modulus. For example, the code
+
+@racketblock[(with-modulus n
+               ((modexpt a b) . mod= . c))]
+
+corresponds with the mathematical statement
+@italic{a}@superscript{@italic{b}} = @italic{c} (mod @italic{n}).
+
+The current modulus is stored in a @tech{parameter} that, for performance reasons, can only be
+set using @racket[with-modulus]. (The basic modular operators cache parameter reads, and this
+restriction guarantees that the cached values are current.)
+
+@defform[(with-modulus n body ...)
+         #:contracts ([n Integer])]{
+Alters the current modulus within the dynamic extent of @racket[body].
+The expression @racket[n] must evaluate to a positive integer.
+
+By default, the current modulus is @racket[1], meaning that every modular arithmetic expression
+that does not raise an error returns @racket[0].
+}
+
+@defproc[(current-modulus) Positive-Integer]{
+Returns the current modulus.
+@examples[#:eval untyped-eval
+                 (current-modulus)
+                 (with-modulus 5 (current-modulus))]
+}
+
+@defproc[(mod [x Exact-Rational]) Natural]{
+Converts a rational number @racket[x] to a natural number less than the current modulus.
+
+If @racket[x] is an integer, this is equivalent to @racket[(modulo x n)].
+If @racket[x] is a fraction, an integer input is generated by multiplying its numerator
+by its denominator's modular inverse.
+
+@examples[#:eval untyped-eval
+                 (with-modulus 7 (mod (* 218 7)))
+                 (with-modulus 7 (mod 3/2))
+                 (with-modulus 7 (mod/ 3 2))
+                 (with-modulus 7 (mod 3/7))]
+}
+
+@deftogether[(@defproc[(mod+ [a Integer] ...) Natural]
+              @defproc[(mod* [a Integer] ...) Natural])]{
+Equivalent to @racket[(modulo (+ a ...) (current-modulus))] and
+@racket[(modulo (* a ...) (current-modulus))], respectively, but generate smaller intermediate
+values.
+}
+
+@deftogether[(@defproc[(modsqr [a Integer]) Natural]
+              @defproc[(modexpt [a Integer] [b Integer]) Natural])]{
+Equivalent to @racket[(mod* a a)] and @racket[(modular-expt a b (current-modulus))], respectively.
+}
+
+@defproc[(mod- [a Integer] [b Integer] ...) Natural]{
+Equivalent to @racket[(modulo (- a b ...) (current-modulus))], but generates smaller intermediate
+values. Note that @racket[(mod- a) = (mod (- a))].
+}
+
+@defproc[(mod/ [a Integer] [b Integer] ...) Natural]{
+Divides @racket[a] by @racket[(* b ...)], by multiplying @racket[a] by the multiplicative inverse
+of @racket[(* b ...)]. The one-argument variant returns the modular inverse of @racket[a].
+
+Note that @racket[(mod/ a b ...)] is @bold{not} equivalent to
+@racket[(modulo (/ a b ...) (current-modulus))]; see @racket[mod=] for a demonstration.
+}
+
+@deftogether[(@defproc[(mod= [a Integer] [b Integer] ...) Boolean]
+              @defproc[(mod< [a Integer] [b Integer] ...) Boolean]
+              @defproc[(mod<= [a Integer] [b Integer] ...) Boolean]
+              @defproc[(mod> [a Integer] [b Integer] ...) Boolean]
+              @defproc[(mod>= [a Integer] [b Integer] ...) Boolean])]{
+Each of these is equivalent to @racket[(op (mod a) (mod b) ...)], where @racket[op] is the
+corresponding numeric comparison function. Additionally, when given one argument, the inequality
+tests always return @racket[#t].
+
+Suppose we wanted to know why 17/4 = 8 (mod 15), but 51/12 (mod 15) is undefined, even though
+normally 51/12 = 17/4. In code,
+@interaction[#:eval untyped-eval
+                    (with-modulus 15 (mod/ 17 4))
+                    (/ 51 12)
+                    (with-modulus 15 (mod/ 51 12))]
+We could try to divide by brute force: find, modulo 15, all the numbers @racket[a]
+for which @racket[(mod* a 4)] is @racket[17], then find all the numbers @racket[b] for which
+@racket[(mod* a 12)] is @racket[51].
+@interaction[#:eval untyped-eval
+                    (with-modulus 15
+                      (for/list ([a  (in-range 15)]
+                                 #:when (mod= (mod* a 4) 17))
+                        a))
+                    (with-modulus 15
+                      (for/list ([b  (in-range 15)]
+                                 #:when (mod= (mod* b 12) 51))
+                        b))]
+So the problem isn't that @racket[b] doesn't exist, it's that @racket[b] isn't @italic{unique}.
+}
 
 @; ----------------------------------------
 @section[#:tag "primes"]{Primes}
 
 
-@defproc[(prime? [z Integer]) boolean?]{
-Returns @racket[#t] if @racket[z] is a prime,
-@racket[#f] otherwise.
+@defproc[(prime? [z Integer]) Boolean]{
+Returns @racket[#t] if @racket[z] is a prime, @racket[#f] otherwise.
 
-Note: An integer @racket[z] is considered a prime, if the only 
-positive divisors of @racket[z] are @racket[1] and @racket[|z|].
+Formally, an integer @racket[z] is prime when the only positive divisors of @racket[z]
+are @racket[1] and @racket[(abs z)].
 
 The positive primes below 20 are:
   @interaction[#:eval untyped-eval
-                      (require racket/list)
                       (filter prime? (range 1 21))]
 The corresponding negative primes are:
   @interaction[#:eval untyped-eval
                       (filter prime? (range 1 -21 -1))]
 }
 
-@defproc[(odd-prime? [z Integer]) boolean?]{
+@defproc[(odd-prime? [z Integer]) Boolean]{
 Returns @racket[#t] if @racket[z] is a odd prime,
 @racket[#f] otherwise.
 
@@ -181,15 +296,15 @@ Returns @racket[#t] if @racket[z] is a odd prime,
                     (odd-prime? 3)]
 }
 
-@defproc[(nth-prime [n Natural]) natural?]{
-Returns the n'th positive prime. 
+@defproc[(nth-prime [n Integer]) Natural]{
+Returns the @racket[n]th positive prime; @racket[n] must be nonnegative.
 @interaction[#:eval untyped-eval
                     (nth-prime 0)
                     (nth-prime 1)
                     (nth-prime 2)]
 }
 
-@defproc[(next-prime [z Integer]) prime?]{
+@defproc[(next-prime [z Integer]) Integer]{
 Returns the first prime larger than @racket[z].
 
 @interaction[#:eval untyped-eval
@@ -197,7 +312,7 @@ Returns the first prime larger than @racket[z].
                     (next-prime 5)]
 }
 
-@defproc[(prev-prime [z Integer]) prime?]{
+@defproc[(prev-prime [z Integer]) Integer]{
 Returns the first prime smaller than @racket[z].
 
 @interaction[#:eval untyped-eval
@@ -205,21 +320,21 @@ Returns the first prime smaller than @racket[z].
                     (prev-prime 5)]
 }
 
-@defproc[(next-primes [z Integer] [n Natural]) (Listof prime?)]{
-Returns list of the next @racket[n] primes larger than @racket[z].
+@defproc[(next-primes [z Integer] [n Integer]) (Listof Integer)]{
+Returns list of the next @racket[n] primes larger than @racket[z]; @racket[n] must be nonnegative.
 
 @interaction[#:eval untyped-eval
                     (next-primes 2 4)]
 }
 
-@defproc[(prev-primes [z Integer] [n Natural]) (Listof prime?)]{
-Returns list of the next @racket[n] primes smaller than @racket[z].
+@defproc[(prev-primes [z Integer] [n Integer]) (Listof Integer)]{
+Returns list of the next @racket[n] primes smaller than @racket[z]; @racket[n] must be nonnegative.
 
 @interaction[#:eval untyped-eval
                     (prev-primes 13 4)]
 }
 
-@defproc[(factorize [n Natural]) (Listof (List prime? natural?))]{
+@defproc[(factorize [n Natural]) (Listof (List Natural Natural))]{
 Returns the factorization of a natural number @racket[n].
 The factorization consists of a list of corresponding 
 primes and exponents. The primes will be in ascending order.
@@ -229,7 +344,7 @@ The prime factorization of 600 = 2^3 * 3^1 * 5^2:
                     (factorize 600)]
 }
 
-@defproc[(defactorize [f (Listof (List prime? natural?))]) natural?]{
+@defproc[(defactorize [f (Listof (List Natural Natural))]) Natural]{
 Returns the natural number, whose factorization is given 
 by @racket[f]. The factorization @racket[f] is represented
 as described in @racket[factorize].
@@ -247,7 +362,7 @@ The divisors appear in ascending order.
                      (divisors -120)]
 }
 
-@defproc[(prime-divisors [z Integer]) (Listof Natural)]{
+@defproc[(prime-divisors [z Natural]) (Listof Natural)]{
 Returns a list of all positive prime divisors of the integer 
 @racket[z]. The divisors appear in ascending order.                                                       
                                                        
@@ -255,10 +370,10 @@ Returns a list of all positive prime divisors of the integer
                      (prime-divisors 120)]
 }
 
-@defproc[(prime-exponents [z Integer]) (Listof Natural)]{
+@defproc[(prime-exponents [z Natural]) (Listof Natural)]{
 Returns a list of the exponents of in a factorization of the integer
 @racket[z].                                                       
-                                                       
+
  @interaction[#:eval untyped-eval
                      (define z (* 2 2 2 3 5 5))
                      (prime-divisors z)
@@ -268,20 +383,19 @@ Returns a list of the exponents of in a factorization of the integer
 @; ----------------------------------------
 @section[#:tag "roots"]{Roots}
 
-
-@defproc[(integer-root [n Natural] [m Natural]) natural?]{
-Returns the @racket[m]'th integer root of @racket[n].
+@defproc[(integer-root [n Natural] [m Natural]) Natural]{
+Returns the @racket[m]th integer root of @racket[n].
 This is the largest number @racket[r] such that 
-@racket[r^m<=n].
-            
+@racket[(expt r m) <= n].
+
  @interaction[#:eval untyped-eval
                      (integer-root (expt 3 4) 4)
                      (integer-root (+ (expt 3 4) 1) 4)]
 }
- 
+
 @defproc[(integer-root/remainder [n Natural] [m Natural]) 
-         (values natural? natural?)]{
-Returns two values. The first, @racket[r], is the @racket[m]'th 
+         (values Natural Natural)]{
+Returns two values. The first, @racket[r], is the @racket[m]th 
 integer root of @racket[n]. The second is @racket[n-r^m].
             
  @interaction[#:eval untyped-eval
@@ -293,31 +407,31 @@ integer root of @racket[n]. The second is @racket[n-r^m].
 @; ----------------------------------------
 @section[#:tag "powers"]{Powers}
 
-@defproc[(max-dividing-power [a Integer] [b Integer]) natural?]{
+@defproc[(max-dividing-power [a Integer] [b Integer]) Natural]{
 Returns the largest exponent, @racket[n], of a power with 
 base @racket[a] that divides @racket[b].
 
-That is, @racket[a^n] divides @racket[b] but @racket[a^(n+1)] does not divide
+That is, @racket[(expt a n)] divides @racket[b] but @racket[(expt a (+ n 1))] does not divide
 @racket[b].
-            
+
  @interaction[#:eval untyped-eval
                      (max-dividing-power 3 (expt 3 4))
                      (max-dividing-power 3 5)]
 }
 
 @defproc[(perfect-power [m Integer]) 
-         (Union (List natural? natural?) #f)]{
+         (U (List Natural Natural) #f)]{
 If @racket[m] is a perfect power, a list with two elements 
-@racket[b] and @racket[n] such that @racket[b^n = m] 
+@racket[b] and @racket[n] such that @racket[(expt b n) = m] 
 is returned, otherwise @racket[#f] is returned.
-            
+
  @interaction[#:eval untyped-eval
                      (perfect-power (expt 3 4))
                      (perfect-power (+ (expt 3 4) 1))]
 }
+
  
- 
-@defproc[(perfect-power? [m Integer]) boolean?]{
+@defproc[(perfect-power? [m Integer]) Boolean]{
 Returns @racket[#t] if @racket[m] is a perfect power,
 otherwise @racket[#f].        
 
@@ -326,10 +440,10 @@ otherwise @racket[#f].
                       (perfect-power? (+ (expt 3 4) 1))]
 }
 
- 
+
 @defproc[(prime-power [m Natural])
-         (Union (List prime? natural?) #f)]{
-If @racket[m] is a power of the form @racket[p^n]
+         (U (List Natural Natural) #f)]{
+If @racket[m] is a power of the form @racket[(expt p n)]
 where @racket[p] is prime, then a list with the
 prime and the exponent is returned, otherwise
 @racket[#f] is returned.
@@ -339,7 +453,7 @@ prime and the exponent is returned, otherwise
                       (prime-power (expt 6 4))]
 }
 
-@defproc[(prime-power? [m Natural]) boolean?]{
+@defproc[(prime-power? [m Natural]) Boolean]{
 Returns @racket[#t] if @racket[m] is a prime power,
 otherwise @racket[#f].
 
@@ -350,7 +464,7 @@ otherwise @racket[#f].
                       (prime-power? 0)]
 }
 
-@defproc[(odd-prime-power? [m Natural]) boolean?]{
+@defproc[(odd-prime-power? [m Natural]) Boolean]{
 Returns @racket[#t] if @racket[m] is a power of an odd prime,
 otherwise @racket[#f].
 
@@ -361,10 +475,10 @@ otherwise @racket[#f].
 }
 
 @defproc[(as-power [m Positive-Integer]) 
-         (values natural? natural?)]{
+         (values Natural Natural)]{
 Returns two values @racket[b] and @racket[n]
-such that @racket[m=b^r] and @racket[n] is maximal.
-                                     
+such that @racket[m = (expt b n)] and @racket[n] is maximal.
+
   @interaction[#:eval untyped-eval
                       (as-power (* (expt 2 4) (expt 3 4)))
                       (expt 6 4)
@@ -373,9 +487,9 @@ such that @racket[m=b^r] and @racket[n] is maximal.
 }
 
 @defproc[(perfect-square [m Natural]) 
-         (Union natural? #f)]{
-Returns @racket[sqrt(m)] if @racket[m] is perfect 
-square, otherwise @racket[#f].        
+         (U Natural #f)]{
+Returns @racket[(sqrt m)] if @racket[m] is perfect 
+square, otherwise @racket[#f].
 
 @interaction[#:eval untyped-eval
                     (perfect-square 9)
@@ -385,42 +499,28 @@ square, otherwise @racket[#f].
 @; ----------------------------------------
 @section[#:tag "multiplicative"]{Multiplicative Functions}
 
-In number theory a multiplicative function is a 
-function @racket[f] such that @racket[f(a b) = f(a) f(b)]
-for all coprime natural numbers @racket[a] and @racket[b].
-
-The functions @racket[totient], @racket[moebius-mu], and, 
-@racket[divisor-sum] are multiplicative.
+The functions in this section are @deftech{multiplicative}.
+In number theory, a multiplicative function is a function @racket[f] such that
+@racket[(f a b) = (* (f a) (f b))] for all coprime natural numbers @racket[a] and @racket[b].
 
 @margin-note{Wikipedia: @hyperlink["http://en.wikipedia.org/wiki/Euler%27s_totient_function"]{Euler's Totient}}
-@defproc[(totient [n Natural]) natural?]{
+@defproc[(totient [n Natural]) Natural]{
 Returns the number of integers from 1 to @racket[n]
 that are coprime with @racket[n].
 
 This function is known as Eulers totient or phi function.
 
-Note: The function @racket[totient] is multiplicative.
-
 @interaction[#:eval untyped-eval
-                    (require racket/function) ; for curry
                     (totient 9)
                     (length (filter (curry coprime? 9) (range 10)))]
 }
 
-
-
-
-@defproc[(moebius-mu [n Natural]) (Union -1 0 1)]{
 @margin-note{Wikipedia: @hyperlink["http://en.wikipedia.org/wiki/M%C3%B6bius_function"]{Moebius Function}}
+@defproc[(moebius-mu [n Natural]) (U -1 0 1)]{
 Returns:
-
-@racket[1]  if @racket[n] is a product of an even number of primes
-
-@racket[-1] if @racket[n] is a product of an odd number of primes
-
-@racket[0]  if @racket[n] has a multiple prime factor
- 
-Note: The function @racket[moebius-mu] is multiplicative.
+@itemlist[@item{@racket[1]  if @racket[n] is a product of an even number of primes}
+          @item{@racket[-1] if @racket[n] is a product of an odd number of primes}
+          @item{@racket[0]  if @racket[n] has a multiple prime factor}]
 
 @interaction[#:eval untyped-eval
                     (moebius-mu (* 2 3 5))
@@ -430,12 +530,10 @@ Note: The function @racket[moebius-mu] is multiplicative.
 
 
 @margin-note{Wikipedia: @hyperlink["http://en.wikipedia.org/wiki/Divisor_function"]{Divisor Function}}
-@defproc[(divisor-sum [n Natural] [k Natural]) natural?]{
+@defproc[(divisor-sum [n Natural] [k Natural]) Natural]{
 Returns sum of the @racket[k]th powers of 
 all divisors of @racket[n].
 
-Note: The function @racket[divisor-sum] is multiplicative.
-
 @interaction[#:eval untyped-eval         
                     (divisor-sum 12 2)
                     (apply + (map sqr (divisors 12)))]
@@ -446,110 +544,118 @@ Note: The function @racket[divisor-sum] is multiplicative.
 @section[#:tag "number-sequences"]{Number Sequences}
 
 @margin-note{Wikipedia: @hyperlink["http://en.wikipedia.org/wiki/Bernoulli_number"]{Bernoulli Number}}
-@defproc[(bernoulli [n Natural]) exact-rational?]{
-  Returns the @racket[n]th Bernoulli number.
-
+@defproc[(bernoulli [n Integer]) Exact-Rational]{
+  Returns the @racket[n]th Bernoulli number; @racket[n] must be nonnegative.
 
   @interaction[#:eval untyped-eval
                       (map bernoulli (range 9))]
+  
+  Note that these are the @italic{first} Bernoulli numbers, since @racket[(bernoulli 1) = -1/2].
 }
 
 @margin-note{MathWorld: @hyperlink["http://mathworld.wolfram.com/EulerianNumber.html"]{Eulerian Number}}
-@defproc[(eulerian-number [n Natural] [k Natural]) natural?]{
-  Returns the Eulerian number @math-style{<n,k>}.
+@defproc[(eulerian-number [n Integer] [k Integer]) Natural]{
+  Returns the Eulerian number @math-style{<n,k>}; both arguments must be nonnegative.
 
-  @interaction[(require math racket)
-               (eulerian-number 5 2)]
+  @interaction[#:eval untyped-eval
+                      (eulerian-number 5 2)]
 }
 
 @margin-note{Wikipedia: @hyperlink["http://en.wikipedia.org/wiki/Fibonacci_number"]{Fibonacci Number}}
-@defproc[(fibonacci [n Natural]) natural?]{
-  Returns the @racket[n]th Fibonacci number.
+@defproc[(fibonacci [n Integer]) Natural]{
+  Returns the @racket[n]th Fibonacci number; @racket[n] must be nonnegative.
 
   The ten first Fibonacci numbers.
-  @interaction[(require math racket)
-               (map fibonacci (range 10))]
+  @interaction[#:eval untyped-eval
+                      (map fibonacci (range 10))]
 }
 
-@defproc[(fibonacci/mod [n Natural] [m Natural]) natural?]{
-  Returns the @racket[n]th Fibonacci number modulo @racket[m].
+@defproc[(fibonacci/mod [n Integer] [m Integer]) Natural]{
+  Returns the @racket[n]th Fibonacci number modulo @racket[m]; @racket[n] must be nonnegative
+  and @racket[m] must be positive.
 
   The ten first Fibonacci numbers modulo 5.
-  @interaction[(require math racket)
-               (map (λ (n) (fibonacci/mod n 5)) (range 10))]
+  @interaction[#:eval untyped-eval
+                      (map (λ (n) (fibonacci/mod n 5)) (range 10))]
 }
 
-@defproc[(farey [n Natural]) (listof rational?)]{
-Returns a list of the numbers in the @racket[n]th Farey sequence.
+@defproc[(farey [n Integer]) (Listof Exact-Rational)]{
+Returns a list of the numbers in the @racket[n]th Farey sequence; @racket[n] must be positive.
+
 The @racket[n]th Farey sequence is the sequence of all 
 completely reduced rational numbers from 0 to 1 which denominators
 are less than or equal to @racket[n].
-  @interaction[(require math)
-               (farey 1)
-               (farey 2)
-               (farey 3)]
+  @interaction[#:eval untyped-eval
+                      (farey 1)
+                      (farey 2)
+                      (farey 3)]
 }
 
 @margin-note{MathWorld: @hyperlink["http://mathworld.wolfram.com/TangentNumber.html"]{Tangent Number}}
-@defproc[(tangent-number [n integer?]) integer?]{
-Returns the @racket[n]th tangent number.
+@defproc[(tangent-number [n Integer]) Integer]{
+Returns the @racket[n]th tangent number; @racket[n] must be nonnegative.
             
-  @interaction[(require math)
-               (tangent-number 1)
-               (tangent-number 2)
-               (tangent-number 3)]
+  @interaction[#:eval untyped-eval
+                      (tangent-number 1)
+                      (tangent-number 2)
+                      (tangent-number 3)]
 }
 
 
 @; ----------------------------------------
 @section[#:tag "combinatorics"]{Combinatorics}
 
-@defproc[(factorial [n Natural]) natural?]{
-  Returns the factorial of @racket[n].
-  The factorial of @racket[n] is the 
-  number @math-style{n!=n*(n-1)*(n-2)*...*1}.
-  @interaction[(require math racket)
-               (factorial 3)
-               (factorial 0)]
+@defproc[(factorial [n Integer]) Natural]{
+  Returns the factorial of @racket[n], which must be nonnegative.
+  The factorial of @racket[n] is the number @racket[(* n (- n 1) (- n 2) ... 1)].
+  @interaction[#:eval untyped-eval
+                      (factorial 3)
+                      (factorial 0)]
 }
 
-@defproc[(binomial [n Natural] [k Natural]) natural?]{
-  Returns @racket[n] choose @racket[k].
-  The binomial coeffecient is given by 
-  @math-style{C(n,k)=n!/(n!(n-k)!)}.
-  @interaction[(require math racket)
-               (binomial 5 3)]
+@defproc[(binomial [n Integer] [k Integer]) Natural]{
+  Returns the number of ways to choose a @italic{set} of @racket[k] items from a set of
+  @racket[n] items; i.e. the order of the @racket[k] items is not significant.
+  Both arguments must be nonnegative.
+  
+  When @racket[k > n], @racket[(binomial n k) = 0]. Otherwise, @racket[(binomial n k)] is
+  equivalent to @racket[(/ (factorial n) (factorial k) (factorial (- n k)))], but computed more
+  quickly.
+  @interaction[#:eval untyped-eval
+                      (binomial 5 3)]
 }
 
-@defproc[(permutations [n Natural] [k Natural]) natural?]{
-  Returns the number of @racket[k]-permutations of @racket[n].
-  That is the number of sequences of length @racket[k] where the 
-  elements are drawn from a set with @racket[n] elements.
-  @math-style{P(n,k)=n!/(n-k)!}.
-  @interaction[(require math racket)
-               (permutations 5 3)]
+@defproc[(permutations [n Integer] [k Integer]) Natural]{
+  Returns the number of ways to choose a @italic{sequence} of @racket[k] items from a set of
+  @racket[n] items; i.e. the order of the @racket[k] items is significant.
+  Both arguments must be nonnegative.
+  
+  When @racket[k > n], @racket[(permutations n k) = 0]. Otherwise, @racket[(permutations n k)] is
+  equivalent to @racket[(/ (factorial n) (factorial (- n k)))].
+  @interaction[#:eval untyped-eval
+                      (permutations 5 3)]
 }
 
-@defproc[(multinomial [n Natural] [ks (Listof Natural)]) natural?]{
-  Returns the multinomial coeffecient.
-  The expression @racket[(multinomial n (list k0 k1 ...))] 
-  returns the number @math-style{n! / (k0! * k1! * ...)}.
-
-  @interaction[(require math racket)
-               (multinomial 5 3 2)]
+@defproc[(multinomial [n Integer] [ks (Listof Integer)]) Natural]{
+  A generalization of @racket[binomial] to multiple sets of choices; i.e.
+  @racket[(multinomial n (list k0 k1))] is the number of ways to choose a set of @racket[k0] items
+  and a set of @racket[k1] items from a set of @racket[n] items. All arguments must be nonnegative.
+  
+  When @racket[(apply + ks) = n], this is equivalent to
+  @racket[(apply / (factorial n) (map factorial ks))]. Otherwise, it returns @racket[0].
+  @interaction[#:eval untyped-eval
+                      (multinomial 5 3 2)]
 }
 
-
-
 @margin-note{Wikipedia: @hyperlink["http://en.wikipedia.org/wiki/Partition_(number_theory)"]{Partition}}
-@defproc[(partition-count [n Natural]) natural?]{
-  Returns the number of partitions of @racket[n].
+@defproc[(partition-count [n Integer]) Natural]{
+  Returns the number of partitions of @racket[n], which must be nonnegative.
   A partition of a positive integer @racket[n] is a way 
   of writing @racket[n] as a sum of positive integers.
-  The number 3 has the partitions @math-style{1+1+1, 1+2, 3}.
-  @interaction[(require math racket)
-               (partition-count 3)
-               (partition-count 4)]
+  The number 3 has the partitions @racket[(+ 1 1 1)], @racket[(+ 1 2)] and @racket[(+ 3)].
+  @interaction[#:eval untyped-eval
+                      (partition-count 3)
+                      (partition-count 4)]
 }
 
 
@@ -558,12 +664,12 @@ Returns the @racket[n]th tangent number.
 
 @subsection{Polygonal Numbers}
 
-@defproc[(triangle? [n Natural]) boolean?]{}
-@defproc[(square? [n Natural]) boolean?]{}
-@defproc[(pentagonal? [n Natural]) boolean?]{}
-@defproc[(hexagonal? [n Natural]) boolean?]{}
-@defproc[(heptagonal? [n Natural]) boolean?]{}
-@defproc[(octagonal? [n Natural]) boolean?]{
+@defproc[(triangle? [n Natural]) Boolean]{}
+@defproc[(square? [n Natural]) Boolean]{}
+@defproc[(pentagonal? [n Natural]) Boolean]{}
+@defproc[(hexagonal? [n Natural]) Boolean]{}
+@defproc[(heptagonal? [n Natural]) Boolean]{}
+@defproc[(octagonal? [n Natural]) Boolean]{
 The functions 
 @racket[triangle?], @racket[square?], @racket[pentagonal?],
 @racket[hexagonal?],@racket[heptagonal?] and @racket[octagonal?] 
@@ -572,12 +678,12 @@ triangle, square, pentagonal, hexagonal, heptagonal and octogonal
 respectively.
 }
 
-@defproc[(triangle [n Natural]) natural?]{}
-@defproc[(sqr [n Natural]) natural?]{}
-@defproc[(pentagonal [n Natural]) natural?]{}
-@defproc[(hexagonal [n Natural]) natural?]{}
-@defproc[(heptagonal [n Natural]) natural?]{}
-@defproc[(octagonal [n Natural]) natural?]{
+@defproc[(triangle [n Natural]) Natural]{}
+@defproc[(sqr [n Natural]) Natural]{}
+@defproc[(pentagonal [n Natural]) Natural]{}
+@defproc[(hexagonal [n Natural]) Natural]{}
+@defproc[(heptagonal [n Natural]) Natural]{}
+@defproc[(octagonal [n Natural]) Natural]{
 The functions @racket[triangle], @racket[sqr], @racket[pentagonal],
 @racket[hexagonal],@racket[heptagonal] and @racket[octagonal] 
 return the @racket[n]th polygonal number of the corresponding
@@ -588,12 +694,12 @@ type of polygonal number.
 @; ----------------------------------------
 
 @section[#:tag "fractions"]{Fractions}
-@defproc[(mediant [x Rational] [y Rational]) rational?]{
+@defproc[(mediant [x Exact-Rational] [y Exact-Rational]) Exact-Rational]{
 Computes the @racket[mediant] of the numbers @racket[x] and @racket[y].
 The mediant of two fractions @math-style{p/q} and @math-style{r/s} in their
 lowest term is the number @math-style{(p+r)/(q+s)}.
-  @interaction[(require math)
-               (mediant 1/2 5/6)]
+  @interaction[#:eval untyped-eval
+                      (mediant 1/2 5/6)]
 }
 
 
@@ -601,26 +707,26 @@ lowest term is the number @math-style{(p+r)/(q+s)}.
 @; ----------------------------------------
 @section[#:tag "quadratics"]{The Quadratic Equation}
 
-@defproc[(quadratic-solutions [a Real] [b Real] [c Real]) (listof Real)]{
+@defproc[(quadratic-solutions [a Real] [b Real] [c Real]) (Listof Real)]{
 Returns a list of all real solutions to the equation @math-style{a x^2 + b x +c = 0}.
-  @interaction[(require math)
-               (quadratic-solutions 1 0 -1)
-               (quadratic-solutions 1 2 1)
-               (quadratic-solutions 1 0 1)]  
+  @interaction[#:eval untyped-eval
+                      (quadratic-solutions 1 0 -1)
+                      (quadratic-solutions 1 2 1)
+                      (quadratic-solutions 1 0 1)]  
 }
 
-@defproc[(quadratic-integer-solutions [a Real] [b Real] [c Real]) (listof Integer)]{
+@defproc[(quadratic-integer-solutions [a Real] [b Real] [c Real]) (Listof Integer)]{
 Returns a list of all integer solutions to the equation @math-style{a x^2 + b x +c = 0}.
-  @interaction[(require math)
-               (quadratic-integer-solutions 1 0 -1)
-               (quadratic-integer-solutions 1 0 -2)]  
+  @interaction[#:eval untyped-eval
+                      (quadratic-integer-solutions 1 0 -1)
+                      (quadratic-integer-solutions 1 0 -2)]  
 }
 
-@defproc[(quadratic-natural-solutions [a Real] [b Real] [c Real]) (listof Natural)]{
+@defproc[(quadratic-natural-solutions [a Real] [b Real] [c Real]) (Listof Natural)]{
 Returns a list of all natural solutions to the equation @math-style{a x^2 + b x +c = 0}.
-  @interaction[(require math)
-               (quadratic-natural-solutions 1 0 -1)
-               (quadratic-natural-solutions 1 0 -2)]  
+  @interaction[#:eval untyped-eval
+                      (quadratic-natural-solutions 1 0 -1)
+                      (quadratic-natural-solutions 1 0 -2)]  
 }
 
 
@@ -642,64 +748,68 @@ Note that @math-style{g} is a primitive root if and only if @math-style{order(g)
 where @math-style{phi} is Eulers totient. A group with a generator is called @emph{cyclic}.
 
 
-@defproc[(unit-group [n Natrual]) (listof Natural)]{
-Returns a list of all elements of @math-style{Un}, the unit group modulo @racket[n].
-  @interaction[(require math)
-               (unit-group 5)
-               (unit-group 6)]  
+@defproc[(unit-group [n Integer]) (Listof Positive-Integer)]{
+Returns a list of all elements of @math-style{Un}, the unit group modulo @racket[n]. The
+modulus @racket[n] must be positive.
+  @interaction[#:eval untyped-eval
+                      (unit-group 5)
+                      (unit-group 6)]  
 }
 
-@defproc[(order [x Natural] [n Natural]) natural?]{
-Returns the order of @racket[x] in the group @math-style{Un}.
-Note: @racket[x] is in @math-style{Un} if and only if @racket[(gcd x n)] is 1.
-  @interaction[(require math)
-               (order 2 5)
-               (order 2 6)]  
+@defproc[(order [x Integer] [n Integer]) Positive-Integer]{
+Returns the order of @racket[x] in the group @math-style{Un}; both arguments must be positive.
+If @racket[x] and @racket[n] are not coprime, @racket[(order x n)] raises an error.
+  @interaction[#:eval untyped-eval
+                      (order 2 5)
+                      (order 2 6)]  
 }
 
-@defproc[(orders [n Natural]) (listof natural?)]{
-Returns a list @racket[(list (order x0) (order x1) ...)] where
+@defproc[(orders [n Integer]) (Listf Positive-Integer)]{
+Returns a list @racket[(list (order x0 n) (order x1 n) ...)] where
 @racket[x0], @racket[x1], ... are the elements of @math-style{Un}.
-  @interaction[(require math racket)
-               (orders 5)
-               (map (curryr order 5) (unit-group 5))]
+The modulus @racket[n] must be positive.
+  @interaction[#:eval untyped-eval
+                      (orders 5)
+                      (map (curryr order 5) (unit-group 5))]
 }
 
-@defproc[(primitive-root? [x Natural] [n Natural]) boolean?]{
+@defproc[(primitive-root? [x Integer] [n Integer]) Boolean]{
 Returns @racket[#t] if the element @racket[x] in @math-style{Un} is a primitive root modulo @racket[n],
-otherwise @racket[#f] is returned. An error is signaled if @racket[x] is not a member of @math-style{Un}.       
-  @interaction[(require math)
-               (primitive-root? 1 5)
-               (primitive-root? 2 5)
-               (primitive-root? 5 5)]
+otherwise @racket[#f] is returned. An error is signaled if @racket[x] is not a member of @math-style{Un}.
+Both arguments must be positive.
+  @interaction[#:eval untyped-eval
+                      (primitive-root? 1 5)
+                      (primitive-root? 2 5)
+                      (primitive-root? 5 5)]
 }
 
-@defproc[(exists-primitive-root? [n Natural]) boolean?]{
+@defproc[(exists-primitive-root? [n Integer]) Boolean]{
 Returns @racket[#t] if the group @math-style{Un} has a primitive root (i.e. it is cyclic),
-otherwise @racket[#f] is returned.        
+otherwise @racket[#f] is returned.
 In other words, @racket[#t] is returned if @racket[n] is one of 
 @math-style{1, 2, 4, p^e, 2*p^e} where @math-style{p} is an odd prime,
 and @racket[#f] otherwise.
-  @interaction[(require math)               
-               (exists-primitive-root? 5)
-               (exists-primitive-root? 6)
-               (exists-primitive-root? 12)]  
+The modulus @racket[n] must be positive.
+  @interaction[#:eval untyped-eval
+                      (exists-primitive-root? 5)
+                      (exists-primitive-root? 6)
+                      (exists-primitive-root? 12)]  
 }
 
-@defproc[(primitive-root [n Natural]) (Union natural? #f)]{
+@defproc[(primitive-root [n Integer]) (Union Natural #f)]{
 Returns a primitive root of @math-style{Un} if one exists,
-otherwise @racket[#f] is returned.
-  @interaction[(require math)
-               (primitive-root 5)
-               (primitive-root 6)]
+otherwise @racket[#f] is returned. The modulus @racket[n] must be positive.
+  @interaction[#:eval untyped-eval
+                      (primitive-root 5)
+                      (primitive-root 6)]
 }
 
-@defproc[(primitive-roots [n Natural]) (Listof natural?)]{
-Returns a list of all primitive roots of @math-style{Un}.
-  @interaction[(require math)
-               (primitive-roots 3)
-               (primitive-roots 5)
-               (primitive-roots 6)]
+@defproc[(primitive-roots [n Integer]) (Listof Natural)]{
+Returns a list of all primitive roots of @math-style{Un}. The modulus @racket[n] must be positive.
+  @interaction[#:eval untyped-eval
+                      (primitive-roots 3)
+                      (primitive-roots 5)
+                      (primitive-roots 6)]
 }