diff --git a/egison.cabal b/egison.cabal
--- a/egison.cabal
+++ b/egison.cabal
@@ -1,5 +1,5 @@
 Name:                egison
-Version:             3.7.1
+Version:             3.7.2
 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/hs-src/Language/Egison/Core.hs b/hs-src/Language/Egison/Core.hs
--- a/hs-src/Language/Egison/Core.hs
+++ b/hs-src/Language/Egison/Core.hs
@@ -639,7 +639,6 @@
   fn <- evalExpr env fnExpr
   xs <-  mapM (\ms -> applyFunc env fn (Value (makeTuple ms))) (map (\ms -> map toEgison ms) (enumTensorIndices ns))
   case (ns, xs) of
-    ([1], x:[]) -> return $ x
     _ -> fromTensor (Tensor ns (V.fromList xs) [])
 
 evalExpr env (TensorContractExpr fnExpr tExpr) = do
diff --git a/lib/math/analysis/derivative.egi b/lib/math/analysis/derivative.egi
--- a/lib/math/analysis/derivative.egi
+++ b/lib/math/analysis/derivative.egi
@@ -52,11 +52,15 @@
 
 (define $grad ∇)
 
+;(define $taylor-expansion
+;  (lambda [$f $x $a]
+;    (map2 *
+;          (map 1#(/ (** (- x a) %1) (fact %1)) nats0)
+           ;          (map (substitute {[x a]} $) (iterate (∂/∂ $ x) f)))))
+
 (define $taylor-expansion
   (lambda [$f $x $a]
-    (map2 *
-          (map 1#(/ (** (- x a) %1) (fact %1)) nats0)
-          (map (substitute {[x a]} $) (iterate (∂/∂ $ x) f)))))
+    (multivariate-taylor-expansion f [| x |] [| a |])))
 
 (define $maclaurin-expansion (taylor-expansion $ $ 0))
 
diff --git a/lib/math/normalize.egi b/lib/math/normalize.egi
--- a/lib/math/normalize.egi
+++ b/lib/math/normalize.egi
@@ -147,62 +147,86 @@
 (define $rewrite-rule-for-cos-and-sin-expr
   (lambda [$expr]
     (match [expr expr] [math-expr math-expr]
-      {[[<div (+ (* $a (,cos $θ) $mr)
+      {[[<div (+ (* $a (,cos $慮) $mr)
                  $pr1)
               $pr2>
-         (| <div (+ (* _ (| (,cos ,(/ θ 2)) (,sin ,(/ θ 2))) _) _) _>
-            <div _ (+ (* _ (| (,cos ,(/ θ 2)) (,sin ,(/ θ 2))) _) _)>)]
-        (rewrite-rule-for-cos-and-sin-expr (/' (+' (*' a (-' (cos (/ θ 2))^2 (sin (/ θ 2))^2) mr) pr1) pr2))]
-       [[<div (+ (* $a (,sin $θ) $mr)
+         (| <div (+ (* _ (| (,cos ,(/ 慮 2)) (,sin ,(/ 慮 2))) _) _) _>
+            <div _ (+ (* _ (| (,cos ,(/ 慮 2)) (,sin ,(/ 慮 2))) _) _)>)]
+        (rewrite-rule-for-cos-and-sin-expr (/' (+' (*' a (-' (cos (/ 慮 2))^2 (sin (/ 慮 2))^2) mr) pr1) pr2))]
+       [[<div (+ (* $a (,sin $慮) $mr)
                  $pr1)
               $pr2>
-         (| <div (+ (* _ (| (,cos ,(/ θ 2)) (,sin ,(/ θ 2))) _) _) _>
-            <div _ (+ (* _ (| (,cos ,(/ θ 2)) (,sin ,(/ θ 2))) _) _)>)]
-        (rewrite-rule-for-cos-and-sin-expr (/' (+' (*' (*' a 2) (*' (cos (/ θ 2)) (sin (/ θ 2))) mr) pr1) pr2))]
+         (| <div (+ (* _ (| (,cos ,(/ 慮 2)) (,sin ,(/ 慮 2))) _) _) _>
+            <div _ (+ (* _ (| (,cos ,(/ 慮 2)) (,sin ,(/ 慮 2))) _) _)>)]
+        (rewrite-rule-for-cos-and-sin-expr (/' (+' (*' (*' a 2) (*' (cos (/ 慮 2)) (sin (/ 慮 2))) mr) pr1) pr2))]
        [[<div $pr2
-              (+ (* $a (,cos $θ) $mr)
+              (+ (* $a (,cos $慮) $mr)
                  $pr1)>
-         (| <div (+ (* _ (| (,cos ,(/ θ 2)) (,sin ,(/ θ 2))) _) _) _>
-            <div _ (+ (* _ (| (,cos ,(/ θ 2)) (,sin ,(/ θ 2))) _) _)>)]
-        (rewrite-rule-for-cos-and-sin-expr (/' pr2 (+' (*' a (-' (cos (/ θ 2))^2 (sin (/ θ 2))^2) mr) pr1)))]
+         (| <div (+ (* _ (| (,cos ,(/ 慮 2)) (,sin ,(/ 慮 2))) _) _) _>
+            <div _ (+ (* _ (| (,cos ,(/ 慮 2)) (,sin ,(/ 慮 2))) _) _)>)]
+        (rewrite-rule-for-cos-and-sin-expr (/' pr2 (+' (*' a (-' (cos (/ 慮 2))^2 (sin (/ 慮 2))^2) mr) pr1)))]
        [[<div $pr2
-              (+ (* $a (,sin $θ) $mr)
+              (+ (* $a (,sin $慮) $mr)
                  $pr1)>
-         (| <div (+ (* _ (| (,cos ,(/ θ 2)) (,sin ,(/ θ 2))) _) _) _>
-            <div _ (+ (* _ (| (,cos ,(/ θ 2)) (,sin ,(/ θ 2))) _) _)>)]
-        (rewrite-rule-for-cos-and-sin-expr (/' pr2 (+' (*' (*' a 2) (*' (cos (/ θ 2)) (sin (/ θ 2))) mr) pr1)))]
+         (| <div (+ (* _ (| (,cos ,(/ 慮 2)) (,sin ,(/ 慮 2))) _) _) _>
+            <div _ (+ (* _ (| (,cos ,(/ 慮 2)) (,sin ,(/ 慮 2))) _) _)>)]
+        (rewrite-rule-for-cos-and-sin-expr (/' pr2 (+' (*' (*' a 2) (*' (cos (/ 慮 2)) (sin (/ 慮 2))) mr) pr1)))]
        [_ expr]})))
 
 (define $rewrite-rule-for-cos-and-sin-poly
   (lambda [$poly]
     (match poly math-expr
-      {[(+ (* $a (,cos $θ)^,2 $mr)
-           (* ,a (,sin ,θ)^,2 ,mr)
+      {[(+ (* $a (,cos $慮)^,2 $mr)
+           (* ,a (,sin ,慮)^,2 ,mr)
            $pr)
         (rewrite-rule-for-cos-and-sin-poly (+' pr (*' a mr)))]
-       ;       [(+ (* $a (,cos $θ)^,2 $mr)
-                   ;           (* ,(* -1 a) (,sin ,θ)^,2 ,mr)
-                   ;           $pr)
-                ;        (rewrite-rule-for-cos-and-sin-poly (+' pr (*' a (cos (* 2 θ)) mr)))]
-       ;       [(+ (* $a (,cos $θ) (,sin ,θ) $mr)
-                   ;           $pr)
-                ;        (rewrite-rule-for-cos-and-sin-poly (+' pr (*' (/ a 2) (sin (* 2 θ)) mr)))]
        [(+ (* $a $mr)
-           (* ,(* -1 a) (,sin $θ)^,2 ,mr)
+           (* ,(* -1 a) (,sin $慮)^,2 ,mr)
            $pr)
-        (rewrite-rule-for-cos-and-sin-poly (+' pr (*' a (cos θ)^2 mr)))]
+        (rewrite-rule-for-cos-and-sin-poly (+' pr (*' a (cos 慮)^2 mr)))]
        [(+ (* $a $mr)
-           (* ,(* -1 a) (,cos $θ)^,2 ,mr)
+           (* ,(* -1 a) (,cos $慮)^,2 ,mr)
            $pr)
-        (rewrite-rule-for-cos-and-sin-poly (+' pr (*' a (sin θ)^2 mr)))]
-       ; (- 1 (cos (* 2 θ))) = (* 2 (sin θ)^2)
-       ;       [(+ (* $a $mr)
-                   ;           (* ,(* -1 a) (,cos $θ) ,mr)
-                   ;           $pr)
-                ;        (rewrite-rule-for-cos-and-sin-poly (+' pr (*' (* 2 a) (sin (/ θ 2))^2 mr)))]
+        (rewrite-rule-for-cos-and-sin-poly (+' pr (*' a (sin 慮)^2 mr)))]
        [_ poly]})))
 
 (define $rewrite-rule-for-cos-to-sin 1#(map-terms rewrite-rule-for-cos-to-sin-term' %1))
+
+(define $rewrite-rule-for-cos-to-sin-term'
+  (lambda [$term]
+    (match term math-expr
+      {[(* $a (,cos $θ)^,2 $mr)
+        (*' a (-' 1 (sin θ)^2) (rewrite-rule-for-cos-to-sin-term' mr))]
+       [_ term]})))
+
+;;
+;; d
+;;
+
+(define $rewrite-rule-for-d (map-terms rewrite-rule-for-d-term $))
+
+(define $rewrite-rule-for-d-term
+  (lambda [$term]
+    (match term math-expr
+      {[(* _ (,d _) (,d _) _)
+        0]
+       [_ term]})))
+
+;;
+;; ∂/∂
+;;
+
+(define $rewrite-rule-for-∂/∂ (map-polys rewrite-rule-for-∂/∂-poly $))
+
+(define $rewrite-rule-for-∂/∂-poly
+  (lambda [$poly]
+    (match poly math-expr
+      {[(+ (* $a <apply (& $g <symbol $f $subs>) $args>^$n $mr)
+           (* $b <apply <symbol ,f ?1#(eq?/m (multiset something) subs %1)> ,args>^,n ,mr)
+           $pr)
+        (+ (* (+ a b) (`g args)^n mr)
+           pr)]
+              [_ poly]})))
 
 (define $rewrite-rule-for-cos-to-sin-term'
   (lambda [$term]