diff --git a/src/go/core.py b/src/go/core.py
--- a/src/go/core.py
+++ b/src/go/core.py
@@ -62,7 +62,7 @@ class Go:
 		self._fill(EMPTY)
 
 	def _fill(self,filling):
-		for (r,c) in self._helper.continuousArea():
+		for (r,c) in self._helper.getContinuousArea():
 			self.board[r][c]=filling
 
 
diff --git a/src/go/helperboard.py b/src/go/helperboard.py
--- a/src/go/helperboard.py
+++ b/src/go/helperboard.py
@@ -7,31 +7,44 @@ class HelperBoard:
 		self._refBoard=board # Go.board, readonly
 		self._boardSize=len(board)
 		self._board=[[EMPTY]*self._boardSize for i in range(self._boardSize)]
-		self._usedCoords=[0]*(self._boardSize**2)*2
-		self._usedCount=0
+
+		self._visited=[0]*(self._boardSize**2)*2
+		self._visitedCount=0
+		self._libs=[0]*(self._boardSize**2)*2
+		self._libCount=0
 
 	def floodFill(self,filling,r,c,needle=None):
 		if c<0 or c>=self._boardSize or r<0 or r>=self._boardSize: return False # out of range
 		if self._board[r][c]: return False # already visited
 		if self._refBoard[r][c]==needle: return True # found something
-		if self._refBoard[r][c]!=filling: return False # out of area boundary
+		if self._refBoard[r][c]!=filling:
+			if self._refBoard[r][c]==EMPTY: # remember group liberties
+				self._board[r][c]=True
+				self._libs[self._libCount*2]=r
+				self._libs[self._libCount*2+1]=c
+				self._libCount+=1
+			return False # out of area boundary
 		self._board[r][c]=True # set visited
-		self._usedCoords[self._usedCount*2]=r
-		self._usedCoords[self._usedCount*2+1]=c
-		self._usedCount+=1
+		self._visited[self._visitedCount*2]=r
+		self._visited[self._visitedCount*2+1]=c
+		self._visitedCount+=1
 
 		# check neighbors
-		return self.floodFill(filling,r,c-1) or \
-			self.floodFill(filling,r,c+1) or \
-			self.floodFill(filling,r-1,c) or \
-			self.floodFill(filling,r+1,c)
+		return self.floodFill(filling,r,c-1,needle) or \
+			self.floodFill(filling,r,c+1,needle) or \
+			self.floodFill(filling,r-1,c,needle) or \
+			self.floodFill(filling,r+1,c,needle)
 
-	def continuousArea(self):
-		for i in range(self._usedCount):
-			yield (self._usedCoords[i*2],self._usedCoords[i*2+1])
+	def getContinuousArea(self):
+		for i in range(self._visitedCount):
+			yield (self._visited[i*2],self._visited[i*2+1])
 
 	def clear(self):
-		for i in range(self._usedCount):
-			(r,c)=(self._usedCoords[i*2],self._usedCoords[i*2+1])
+		for i in range(self._visitedCount):
+			(r,c)=(self._visited[i*2],self._visited[i*2+1])
 			self._board[r][c]=EMPTY
-		self._usedCount=0
+		self._visitedCount=0
+		for i in range(self._libCount):
+			(r,c)=(self._libs[i*2],self._visited[i*2+1])
+			self._board[r][c]=EMPTY
+		self._libCount=0