diff --git a/nv.c b/nv.c
index 8101a49..e7b16b8 100644
--- a/nv.c
+++ b/nv.c
@@ -72,7 +72,8 @@ int NV_runInteractive(const NV_ID *cTypeList, const NV_ID *opList)
 		tokenList = NV_tokenize(cTypeList, line);
 		NV_convertLiteral(&tokenList, opList);
 		NV_printNodeByID(&tokenList);
-		
+		NV_evaluateSetence(&tokenList);
+		NV_printNodeByID(&tokenList);
 	}
 	return 0;
 }
@@ -151,16 +152,32 @@ int NV_convertLiteral(const NV_ID *tokenizedList, const NV_ID *opList)
 //
 // Evaluate
 //
-/*
 void NV_evaluateSetence(const NV_ID *tokenizedList)
 {
-	int i;
-	NV_ID t;
-	for(i = 0;;){
-		t = 
+	int i, lastOpIndex;
+	int32_t lastOpPrec, opPrec;
+	NV_ID t, lastOp;
+	for(;;){
+		lastOpPrec = -1;
+		for(i = 0; ; i++){
+			t = NV_Array_getByIndex(tokenizedList, i);
+			if(NV_ID_isEqual(&t, &NODEID_NULL)) break;
+			if(!NV_isTreeType(&t, &NODEID_TREE_TYPE_OP)) continue;
+			opPrec = NV_getOpPrecAt(tokenizedList, i);
+			if(lastOpPrec & 1 ? lastOpPrec <= opPrec : lastOpPrec < opPrec){
+				// continue searching
+				lastOpIndex = i;
+				lastOpPrec = opPrec;
+				lastOp = t;
+				continue;
+			}
+			// found. lastOpID is target op.
+			break;
+		}
+		if(lastOpPrec == -1) break;	// no more op
+		NV_tryExecOpAt(tokenizedList, lastOpIndex);
 	}
 }
-*/
 /*
 void NV_evaluateSentence(const NV_ID *tokenizedList)
 {
@@ -206,52 +223,6 @@ void NV_evaluateSentence(const NV_ID *tokenizedList)
 	}
 }
 */
-/*
-void NV_tryExecOp(int32_t *excFlag, NV_Pointer lang, NV_Pointer thisTerm, NV_Pointer vDict, NV_Pointer root)
-{
-	NV_Pointer fallbackOp, op;
-	NV_Pointer orgTerm = thisTerm;
-	//
-	op = NV_ListItem_getData(thisTerm);	
-#ifdef DEBUG
-	if(NV_debugFlag & NV_DBG_FLAG_VERBOSE){
-		NV_DbgInfo("%s", "Begin native op: ");
-		NV_Operator_print(op); putchar('\n');
-	}
-#endif
-	NV_Operator_exec(op, excFlag, lang, vDict, thisTerm);
-#ifdef DEBUG
-	if(NV_debugFlag & NV_DBG_FLAG_VERBOSE){
-		NV_DbgInfo("%s", "End native op:");
-		NV_Operator_print(op); putchar('\n');
-	}
-#endif
-	if(*excFlag & NV_EXC_FLAG_FAILED){
-		// try fallback
-		fallbackOp = NV_Lang_getFallbackOperator(lang, op);
-		if(NV_E_isNullPointer(fallbackOp)){
-			NV_Error("%s", "Operator mismatched: ");
-			NV_Operator_print(op); putchar('\n');
-			NV_List_printAll(root, NULL, NULL, "]\n");
-			return;
-		}
-#ifdef DEBUG
-	if(NV_debugFlag & NV_DBG_FLAG_VERBOSE){
-		NV_DbgInfo("%s", "Fallback found:");
-		NV_Operator_print(fallbackOp); putchar('\n');
-	}
-#endif
-		CLR_FLAG(*excFlag, NV_EXC_FLAG_FAILED);
-		NV_ListItem_setData(orgTerm, fallbackOp);
-		thisTerm = orgTerm;
-	}
-#ifdef DEBUG
-	if(NV_debugFlag & NV_DBG_FLAG_VERBOSE){
-		NV_List_printAll(root, NULL, NULL, "]\n");
-	}
-#endif
-}
-*/
 //
 // main
 //
diff --git a/nv.h b/nv.h
index c173a01..8f762bd 100644
--- a/nv.h
+++ b/nv.h
@@ -75,11 +75,13 @@ int NV_isTreeType(const NV_ID *node, const NV_ID *tType);
 NV_ID NV_tokenize(const NV_ID *cTypeList, const char *input);
 int NV_runInteractive(const NV_ID *cTypeList, const NV_ID *opList);
 int NV_convertLiteral(const NV_ID *tokenizedList, const NV_ID *opList);
+void NV_evaluateSetence(const NV_ID *tokenizedList);
 
 // @nv_array.c
 NV_ID NV_Array_create();
 NV_ID NV_Array_push(const NV_ID *array, const NV_ID *data);
 NV_ID NV_Array_getByIndex(const NV_ID *array, int index);
+void NV_Array_removeIndex(const NV_ID *array, int index);
 void NV_Array_writeToIndex(const NV_ID *array, int index, const NV_ID *data);
 void NV_Array_print(const NV_ID *array);
 
@@ -134,10 +136,12 @@ NV_ID NV_Node_getRelatedNodeFrom(const NV_ID *from, const NV_ID *rel);
 NV_ID NV_Node_createWithString(const char *s);
 void NV_Node_setStrToID(const NV_ID *id, const char *s);
 int NV_Node_String_compare(const NV_Node *na, const NV_Node *nb);
+int NV_Node_String_compareWithCStr(const NV_Node *na, const char *s);
 char *NV_Node_String_strchr(const NV_Node *ns, char c);
 long NV_Node_String_strtol(const NV_Node *ns, int *endptrindex, int base);
 size_t NV_Node_String_strlen(const NV_Node *ns);
 //
+int NV_Node_isInteger(const NV_ID *id);
 NV_ID NV_Node_createWithInt32(int32_t v);
 void NV_Node_setInt32ToID(const NV_ID *id, int32_t v);
 int32_t NV_Node_getInt32FromID(const NV_ID *id);
@@ -147,6 +151,8 @@ int NV_Lang_getCharType(const NV_ID *cTypeList, char c);
 NV_ID NV_createCharTypeList();
 void NV_addOp(const NV_ID *opList, const char *token, int32_t prec, const NV_ID *func);
 NV_ID NV_createOpList();
+int32_t NV_getOpPrecAt(const NV_ID *tList, int index);
+void NV_tryExecOpAt(const NV_ID *tList, int index);
 void NV_Op_print(const NV_ID *op);
 
 // @nv_static.c
diff --git a/nv_array.c b/nv_array.c
index 495b985..895eaf7 100644
--- a/nv_array.c
+++ b/nv_array.c
@@ -44,6 +44,25 @@ NV_ID NV_Array_getByIndex(const NV_ID *array, int index)
 	return NV_Variable_getData(&t);
 }
 
+void NV_Array_removeIndex(const NV_ID *array, int index)
+{
+	NV_ID t, tn, tnn, r;
+	if(index < 0) return;
+	t = *array;
+	for(; index; index--){
+		if(index == 0) break;
+		t = NV_Node_getRelatedNodeFrom(&t, &RELID_ARRAY_NEXT);
+		if(NV_ID_isEqual(&t, &NODEID_NULL)) break;
+	}
+	// tのnextが削除対象。これをtnとおく。
+	if(!NV_ID_isEqual(&t, &NODEID_NULL)){
+		tn = NV_Node_getRelatedNodeFrom(&t, &RELID_ARRAY_NEXT);
+		tnn = NV_Node_getRelatedNodeFrom(&tn, &RELID_ARRAY_NEXT);
+		r = NV_Node_getRelationFrom(&t, &RELID_ARRAY_NEXT);
+		NV_Node_updateRelationTo(&r, &tnn);
+	}
+}
+
 void NV_Array_writeToIndex(const NV_ID *array, int index, const NV_ID *data)
 {
 	NV_ID t;
diff --git a/nv_node.c b/nv_node.c
index 6b8ecdc..8ef5d2e 100644
--- a/nv_node.c
+++ b/nv_node.c
@@ -373,6 +373,15 @@ int NV_Node_String_compare(const NV_Node *na, const NV_Node *nb)
 	return strcmp(na->data, nb->data);
 }
 
+int NV_Node_String_compareWithCStr(const NV_Node *na, const char *s)
+{
+	// compatible with strcmp
+	// but if node->data is null, returns -1.
+	// "" == "" -> true
+	if(!na || !s || na->type != kString) return -1;
+	return strcmp(na->data, s);
+}
+
 char *NV_Node_String_strchr(const NV_Node *ns, char c)
 {
 	if(!ns || ns->type != kString) return NULL;
@@ -402,6 +411,15 @@ size_t NV_Node_String_strlen(const NV_Node *ns)
 // Integer
 //
 
+int NV_Node_isInteger(const NV_ID *id)
+{
+	NV_Node *n;
+	//
+	n = NV_Node_getByID(id);
+	if(!n || n->type != kInteger) return 0;
+	return 1;
+}
+
 NV_ID NV_Node_createWithInt32(int32_t v)
 {
 	NV_ID id;
diff --git a/nv_op.c b/nv_op.c
index 3ce7985..d281bfa 100644
--- a/nv_op.c
+++ b/nv_op.c
@@ -73,6 +73,118 @@ NV_ID NV_createOpList()
 	return opList;
 }
 
+int32_t NV_getOpPrecAt(const NV_ID *tList, int index)
+{
+	NV_ID op = NV_Array_getByIndex(tList, index);
+	NV_ID ePrec = NV_Node_getRelatedNodeFrom(&op, &RELID_OP_PRECEDENCE);
+	return NV_Node_getInt32FromID(&ePrec);
+}
+
+void NV_tryExecOpAt(const NV_ID *tList, int index)
+{
+	NV_ID op = NV_Array_getByIndex(tList, index);
+	NV_ID func = NV_Node_getRelatedNodeFrom(&op, &RELID_OP_FUNC);
+	puts("begin op");
+	NV_printNodeByID(&op);
+	if(NV_Node_String_compareWithCStr(
+		NV_Node_getByID(&func), "NV_Op_nothing") == 0){
+		NV_Array_removeIndex(tList, index);
+	} else if(NV_Node_String_compareWithCStr(
+		NV_Node_getByID(&func), "NV_Op_add") == 0){
+		NV_ID nL, nR, ans;
+		int vL, vR;
+		nL = NV_Array_getByIndex(tList, index - 1);
+		nR = NV_Array_getByIndex(tList, index + 1);
+		if(!NV_Node_isInteger(&nL) || !NV_Node_isInteger(&nR)){
+			NV_ID errObj = NV_Node_createWithString(
+				"Error: Invalid Operand Type.");
+			NV_Array_writeToIndex(tList, index, &errObj);
+			return;
+		}
+		vL = NV_Node_getInt32FromID(&nL);
+		vR = NV_Node_getInt32FromID(&nR);
+		//
+		index--;
+		NV_Array_removeIndex(tList, index);
+		NV_Array_removeIndex(tList, index);
+		//
+		ans = NV_Node_createWithInt32(vL + vR);
+		NV_Array_writeToIndex(tList, index, &ans);
+	} else if(NV_Node_String_compareWithCStr(
+		NV_Node_getByID(&func), "NV_Op_mul") == 0){
+		NV_ID nL, nR, ans;
+		int vL, vR;
+		nL = NV_Array_getByIndex(tList, index - 1);
+		nR = NV_Array_getByIndex(tList, index + 1);
+		if(!NV_Node_isInteger(&nL) || !NV_Node_isInteger(&nR)){
+			NV_ID errObj = NV_Node_createWithString(
+				"Error: Invalid Operand Type.");
+			NV_Array_writeToIndex(tList, index, &errObj);
+			return;
+		}
+		vL = NV_Node_getInt32FromID(&nL);
+		vR = NV_Node_getInt32FromID(&nR);
+		//
+		index--;
+		NV_Array_removeIndex(tList, index);
+		NV_Array_removeIndex(tList, index);
+		//
+		ans = NV_Node_createWithInt32(vL * vR);
+		NV_Array_writeToIndex(tList, index, &ans);
+	} else{
+		NV_ID errObj = NV_Node_createWithString(
+			"Error: Op NOT found or NOT implemented.");
+		NV_Array_writeToIndex(tList, index, &errObj);
+	}
+}
+
+/*
+void NV_tryExecOp(int32_t *excFlag, NV_Pointer lang, NV_Pointer thisTerm, NV_Pointer vDict, NV_Pointer root)
+{
+	NV_Pointer fallbackOp, op;
+	NV_Pointer orgTerm = thisTerm;
+	//
+	op = NV_ListItem_getData(thisTerm);	
+#ifdef DEBUG
+	if(NV_debugFlag & NV_DBG_FLAG_VERBOSE){
+		NV_DbgInfo("%s", "Begin native op: ");
+		NV_Operator_print(op); putchar('\n');
+	}
+#endif
+	NV_Operator_exec(op, excFlag, lang, vDict, thisTerm);
+#ifdef DEBUG
+	if(NV_debugFlag & NV_DBG_FLAG_VERBOSE){
+		NV_DbgInfo("%s", "End native op:");
+		NV_Operator_print(op); putchar('\n');
+	}
+#endif
+	if(*excFlag & NV_EXC_FLAG_FAILED){
+		// try fallback
+		fallbackOp = NV_Lang_getFallbackOperator(lang, op);
+		if(NV_E_isNullPointer(fallbackOp)){
+			NV_Error("%s", "Operator mismatched: ");
+			NV_Operator_print(op); putchar('\n');
+			NV_List_printAll(root, NULL, NULL, "]\n");
+			return;
+		}
+#ifdef DEBUG
+	if(NV_debugFlag & NV_DBG_FLAG_VERBOSE){
+		NV_DbgInfo("%s", "Fallback found:");
+		NV_Operator_print(fallbackOp); putchar('\n');
+	}
+#endif
+		CLR_FLAG(*excFlag, NV_EXC_FLAG_FAILED);
+		NV_ListItem_setData(orgTerm, fallbackOp);
+		thisTerm = orgTerm;
+	}
+#ifdef DEBUG
+	if(NV_debugFlag & NV_DBG_FLAG_VERBOSE){
+		NV_List_printAll(root, NULL, NULL, "]\n");
+	}
+#endif
+}
+*/
+
 void NV_Op_print(const NV_ID *op)
 {
 	NV_ID eFunc;