diff --git a/egison.cabal b/egison.cabal
--- a/egison.cabal
+++ b/egison.cabal
@@ -1,5 +1,5 @@
 Name:                egison
-Version:             4.0.1
+Version:             4.0.2
 Synopsis:            Programming language with non-linear pattern-matching against non-free data
 Description:
   An interpreter for Egison, a **pattern-matching-oriented**, purely functional programming language.
diff --git a/lib/core/number.egi b/lib/core/number.egi
--- a/lib/core/number.egi
+++ b/lib/core/number.egi
@@ -175,3 +175,5 @@
                                 (n / x)
                                 (1 / x))
               in (n, map 3#%3 s, map 3#%3 c)
+
+pi := f.pi
diff --git a/lib/math/common/constants.egi b/lib/math/common/constants.egi
--- a/lib/math/common/constants.egi
+++ b/lib/math/common/constants.egi
@@ -2,7 +2,5 @@
 -- Mathematical constants
 --
 
-pi := π
-
 MinkowskiMetric :=
   [|[|-1, 0, 0, 0|], [|0, 1, 0, 0|], [|0, 0, 1, 0|], [|0, 0, 0, 1|]|]