diff --git a/egison.cabal b/egison.cabal
--- a/egison.cabal
+++ b/egison.cabal
@@ -1,5 +1,5 @@
 Name:                egison
-Version:             3.7.6
+Version:             3.7.7
 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/math/normalize.egi b/lib/math/normalize.egi
--- a/lib/math/normalize.egi
+++ b/lib/math/normalize.egi
@@ -213,12 +213,12 @@
        [_ term]})))
 
 ;;
-;; ∂/∂
+;; d/d
 ;;
 
-(define $rewrite-rule-for-∂/∂ (map-polys rewrite-rule-for-∂/∂-poly $))
+(define $rewrite-rule-for-d/d (map-polys rewrite-rule-for-d/d-poly $))
 
-(define $rewrite-rule-for-∂/∂-poly
+(define $rewrite-rule-for-d/d-poly
   (lambda [$poly]
     (match poly math-expr
       {[(+ (* $a <apply (& $g <symbol $f $subs>) $args>^$n $mr)
@@ -249,12 +249,12 @@
        [_ term]})))
 
 ;;
-;; ∂/∂
+;; d/d
 ;;
 
-(define $rewrite-rule-for-∂/∂ (map-polys rewrite-rule-for-∂/∂-poly $))
+(define $rewrite-rule-for-d/d (map-polys rewrite-rule-for-d/d-poly $))
 
-(define $rewrite-rule-for-∂/∂-poly
+(define $rewrite-rule-for-d/d-poly
   (lambda [$poly]
     (match poly math-expr
       {[(+ (* $a <apply (& $g <symbol $f $subs>) $args>^$n $mr)