diff --git a/src/main/scala/com/fluency03/blockchain/core/Difficulty.scala b/src/main/scala/com/fluency03/blockchain/core/Difficulty.scala
index 2b016de..9328238 100644
--- a/src/main/scala/com/fluency03/blockchain/core/Difficulty.scala
+++ b/src/main/scala/com/fluency03/blockchain/core/Difficulty.scala
@@ -59,7 +59,7 @@ object Difficulty {
     case len => "0" * (64 - len) + hex
   }
 
-  def hashLessThanTarget(hash: String, target: String): Boolean = ???
+//  def hashLessThanTarget(hash: String, target: String): Boolean = ???
 
   def difficultyOf(target: BigInt, negative: Boolean, overflow: Boolean): Double = {
     if (target == 0 || negative || overflow) 0.0
diff --git a/src/test/scala/com/fluency03/blockchain/core/DifficultyTest.scala b/src/test/scala/com/fluency03/blockchain/core/DifficultyTest.scala
index 6cee64b..1dd6170 100644
--- a/src/test/scala/com/fluency03/blockchain/core/DifficultyTest.scala
+++ b/src/test/scala/com/fluency03/blockchain/core/DifficultyTest.scala
@@ -20,13 +20,6 @@ class DifficultyTest extends FlatSpec with Matchers {
     targetOfBits("05009234".hex2Long) shouldEqual "92340000".hex2Long
     targetOfBits("04923456".hex2Long) shouldEqual - "12345600".hex2Long
     targetOfBits("04123456".hex2Long) shouldEqual "12345600".hex2Long
-//    println("1d00ffff".hex)
-//    println(bitsOfTarget(t1, n1))
-//    println(n1, o1)
-//    println(bitsOfTarget(t2, n2))
-//    println(n2, o2)
-//    println(bitsOfTarget(t3, n3))
-//    println(n3, o3)
   }
 
   "padHexTarget" should "add enough zeros (0) in front of a hex fot making it 64 bytes." in {
@@ -34,10 +27,27 @@ class DifficultyTest extends FlatSpec with Matchers {
     padHexTarget(t2.toString(16)) shouldEqual "0000000000012dcd000000000000000000000000000000000000000000000000"
     difficultyOf(t1, n1, o1) shouldEqual 1.0
     difficultyOf(t2, n2, o2) shouldEqual 55589.518126868665
-//    targetOfBits(bitsOfTarget(t1, n1)) shouldEqual t1
-//    targetOfBits(bitsOfTarget(t2, n2)) shouldEqual t2
+    difficultyOf(0, n2, o2) shouldEqual 0
+    difficultyOf(t1, true, o1) shouldEqual 0
+    difficultyOf(t1, n1, true) shouldEqual 0
   }
 
-
+  "getLowBits" should "obtain the N lower bits of a BigInt." in {
+    getLowBits(BigInt(1000), 2) shouldEqual 0
+    getLowBits(BigInt(1001), 2) shouldEqual 1
+    getLowBits(BigInt(1002), 2) shouldEqual 2
+    getLowBits(BigInt(1003), 2) shouldEqual 3
+    getLowBits(BigInt(1004), 2) shouldEqual 0
+    getLowBits(BigInt(1005), 2) shouldEqual 1
+
+    getLowBits(BigInt(1000), 4) shouldEqual 8
+    getLowBits(BigInt(1001), 4) shouldEqual 9
+    getLowBits(BigInt(1002), 4) shouldEqual 10
+    getLowBits(BigInt(1003), 4) shouldEqual 11
+    getLowBits(BigInt(1004), 4) shouldEqual 12
+    getLowBits(BigInt(1005), 4) shouldEqual 13
+
+    getLowBits(BigInt(1000), 8) shouldEqual 232
+  }
 
 }