diff --git a/egison.cabal b/egison.cabal
--- a/egison.cabal
+++ b/egison.cabal
@@ -1,9 +1,9 @@
 Name:                egison
-Version:             3.3.4
-Synopsis:            Programming language with non-linear pattern-matching with backtracking
+Version:             3.3.5
+Synopsis:            Programming language with non-linear pattern-matching against unfree data
 Description:
-  An interpreter for Egison, the programming langugage that realized non-linear pattern-matching with backtracking.
-  With Egison, we can directly represent pattern-matching against lists, multisets, sets, trees, graphs and any kind of data types.
+  An interpreter for Egison, the programming langugage that realized non-linear pattern-matching against unfree data types.
+  With Egison, we can directly represent pattern-matching against a wide range of data types such as lists, multisets, sets, trees and graphs.
   We can find Egison programs in @lib@ and @sample@ directories.
   This package also include Emacs Lisp file @egison-mode.el@ in @elisp@ directory.
   .
@@ -14,7 +14,10 @@
   <<http://www.egison.org/images/poker-hands.png>>
   .
   The pattern-matching of Egison is very powerful.
-  We can use it for pattern-matching against graphs, too.
+  Please view and try more demonstrations.
+  .
+  <http://www.egison.org/demonstrations/>
+  .  
   Egison is not popular at all now.
   Please help us to make Egison popular.
 Homepage:            http://www.egison.org
diff --git a/hs-src/Language/Egison/Primitives.hs b/hs-src/Language/Egison/Primitives.hs
--- a/hs-src/Language/Egison/Primitives.hs
+++ b/hs-src/Language/Egison/Primitives.hs
@@ -255,9 +255,9 @@
 divide :: PrimitiveFunc
 divide = twoArgs $ \val val' -> numberBinaryOp' val val'
  where
-  numberBinaryOp' (Integer i)  (Integer i')  = return $ Rational $ (%) i  i'
+  numberBinaryOp' (Integer i)  (Integer i')  = numberBinaryOp' (Rational (i % 1)) (Rational (i' % 1))
   numberBinaryOp' (Integer i)  val           = numberBinaryOp' (Rational (i % 1)) val
-  numberBinaryOp' val          (Integer i)   = numberBinaryOp' val (Rational (i % 1)) 
+  numberBinaryOp' val          (Integer i)   = numberBinaryOp' val (Rational (i % 1))
   numberBinaryOp' (Rational r) (Rational r') =
     let m = numerator r' in
     let n = denominator r' in
diff --git a/lib/core/natural-number.egi b/lib/core/natural-number.egi
--- a/lib/core/natural-number.egi
+++ b/lib/core/natural-number.egi
@@ -12,7 +12,7 @@
       {[0 {[]}]
        [_ {}]}]
      [<s $> nat
-      {[$tgt (match (compare-integer tgt 0) ordering
+      {[$tgt (match (compare tgt 0) ordering
                {[<greater> {(- tgt 1)}]
                 [_ {}]})]}]
      [$ [something]
diff --git a/lib/core/number.egi b/lib/core/number.egi
--- a/lib/core/number.egi
+++ b/lib/core/number.egi
@@ -15,7 +15,7 @@
       {[<cons $n <nil>> n]
        [<cons $n $rs>
         (let {[$r (min rs)]}
-          (match (compare-integer n r) ordering
+          (match (compare n r) ordering
             {[<less> n]
              [_ r]}))]})))
 
@@ -25,7 +25,7 @@
       {[<cons $n <nil>> n]
        [<cons $n $rs>
         (let {[$r (max rs)]}
-          (match (compare-integer n r) ordering
+          (match (compare n r) ordering
             {[<greater> n]
              [_ r]}))]})))
 
@@ -35,9 +35,9 @@
       {[<cons $n <nil>> [n n]]
        [<cons $n $rs>
         (let {[[$min-n $max-n] (min-and-max rs)]}
-          (match (compare-integer n min-n) ordering
+          (match (compare n min-n) ordering
             {[<less> [n max-n]]
-             [_ (match (compare-integer n max-n) ordering
+             [_ (match (compare n max-n) ordering
                   {[<greater> [min-n n]]
                    [_ [min-n max-n]]})]}))]})))
 
diff --git a/sample/tak.egi b/sample/tak.egi
new file mode 100644
--- /dev/null
+++ b/sample/tak.egi
@@ -0,0 +1,11 @@
+(define $tak
+  (lambda [$x $y $z]
+    (if (lte? x y)
+      y
+      (tak (tak (- x 1) y z)
+           (tak (- y 1) z x)
+           (tak (- z 1) x y)))))
+
+(test (tak 1 1 1))
+
+(test (tak 4 2 1))