diff --git a/include/mcl/bn.hpp b/include/mcl/bn.hpp
index ef1737c..58bfc27 100644
--- a/include/mcl/bn.hpp
+++ b/include/mcl/bn.hpp
@@ -28,7 +28,7 @@ struct CurveParam {
 };
 
 const CurveParam CurveSNARK1 = { 4965661367192848881, 3, 9 };
-const CurveParam CurveSNARK2 = { 4965661367192848881, 82, 9 };
+//const CurveParam CurveSNARK2 = { 4965661367192848881, 82, 9 };
 const CurveParam CurveFp254BNb = { -((1LL << 62) + (1LL << 55) + (1LL << 0)), 2, 1 };
 
 template<class Vec>
@@ -189,6 +189,7 @@ struct ParamT {
 	typedef Fp2T<Fp> Fp2;
 	typedef mcl::EcT<Fp> G1;
 	typedef mcl::EcT<Fp2> G2;
+	bool isCurveFp254BNb;
 	mpz_class z;
 	mpz_class abs_z;
 	bool isNegative;
@@ -223,6 +224,7 @@ struct ParamT {
 
 	void init(const CurveParam& cp = CurveFp254BNb, fp::Mode mode = fp::FP_AUTO)
 	{
+		isCurveFp254BNb = cp == CurveFp254BNb;
 		{
 			uint64_t t = std::abs(cp.z);
 			isNegative = cp.z < 0;
@@ -280,7 +282,7 @@ struct ParamT {
 
 		const mpz_class largest_c = abs(6 * z + 2);
 		useNAF = getGoodRepl(siTbl, largest_c);
-		getGoodRepl(zReplTbl, abs(z)); // QQQ : snark
+		getGoodRepl(zReplTbl, abs(z));
 		exp_c0 = -2 + z * (-18 + z * (-30 - 36 *z));
 		exp_c1 = 1 + z * (-12 + z * (-18 - 36 * z));
 		exp_c2 = 6 * z * z + 1;
@@ -809,16 +811,14 @@ struct BNT {
 		}
 
 	public:
-		// not used
-		void decompress()
+		void decompress() // for test
 		{
 			Fp2 nume, denomi;
 			decompressBeforeInv(nume, denomi);
-			denomi.inverse();
+			Fp2::inv(denomi, denomi);
 			g1_ = nume * denomi; // g1 is recoverd.
 			decompressAfterInv();
 		}
-
 		/*
 			2275clk * 186 = 423Kclk QQQ
 		*/
@@ -872,6 +872,7 @@ struct BNT {
 		*/
 		static void fixed_power(Fp12& z, const Fp12& x)
 		{
+			assert(param.isCurveFp254BNb);
 			Fp12 x_org = x;
 			Fp12 d62;
 			Fp2 c55nume, c55denomi, c62nume, c62denomi;
@@ -902,7 +903,7 @@ struct BNT {
 	static void pow_z(Fp12& y, const Fp12& x)
 	{
 #if 1
-		if (0) {
+		if (param.isCurveFp254BNb) {
 			Compress::fixed_power(y, x);
 		} else {
 			Fp12 orgX = x;
diff --git a/test/bn_test.cpp b/test/bn_test.cpp
index 29830dc..01f4bcf 100644
--- a/test/bn_test.cpp
+++ b/test/bn_test.cpp
@@ -6,6 +6,7 @@ cybozu::CpuClock clk;
 #include <mcl/bn256.hpp>
 #include <cybozu/option.hpp>
 
+typedef mcl::bn256::BN::Compress Compress;
 using namespace mcl::bn256;
 
 mcl::fp::Mode g_mode;
@@ -125,6 +126,40 @@ void testMapToG2()
 	}
 }
 
+void testCyclotomic()
+{
+	Fp12 a;
+	for (int i = 0; i < 12; ++i) {
+		a.getFp0()[i] = i * i;
+	}
+	BN::mapToCyclotomic(a, a);
+	Fp12 d;
+	Compress b(d, a);
+	a *= a;
+	Fp12 d2;
+	Compress c(d2, b);
+	Compress::square_n(c, 1);
+	c.decompress();
+	CYBOZU_TEST_EQUAL(a, d2);
+	Compress::square_n(b, 1);
+	b.decompress();
+	CYBOZU_TEST_EQUAL(a, d);
+}
+
+void testCompress()
+{
+	if (!BN::param.isCurveFp254BNb) return;
+	Fp12 a;
+	for (int i = 0; i < 12; ++i) {
+		a.getFp0()[i] = i;
+	}
+	BN::mapToCyclotomic(a, a);
+	Fp12 b;
+	Compress::fixed_power(b, a);
+	Fp12 c;
+	Fp12::pow(c, a, BN::param.abs_z);
+	CYBOZU_TEST_EQUAL(b, c);
+}
 
 void test(const TestSet& ts)
 {
@@ -185,6 +220,8 @@ CYBOZU_TEST_AUTO(naive)
 		testSetStr(ts);
 		testMapToG1();
 		testMapToG2();
+		testCyclotomic();
+		testCompress();
 		test(ts);
 //break;
 	}