diff --git a/DAS/block.py b/DAS/block.py
index f76a944..45094f8 100644
--- a/DAS/block.py
+++ b/DAS/block.py
@@ -81,3 +81,90 @@ class Block:
             print(line+"|")
         print(dash)
 
+class SparseBlock:
+
+    def __init__(self, size, rows, columns):
+        self.blockSize = size
+        self.rows = {r: zeros(self.blockSize) for r in rows}
+        self.columns = {r: zeros(self.blockSize) for r in columns}
+
+    def fill(self):
+        for line in self.rows:
+            line.setall(1)
+        for line in self.columns:
+            line.setall(1)
+
+    def merge(self, merged):
+        for id in self.rows:
+            self.mergeRow(id, merged.getRow(id))
+        for id in self.columns:
+            self.mergeColumn(id, merged.getColumn(id))
+
+    def getSegment(self, rowID, columnID):
+        """Check whether a segment is included"""
+        ret = 0
+
+        r = self.rows.get(rowID)
+        if r:
+            ret |= r[columnID]
+
+        c = self.columns.get(columnID)
+        if c:
+            ret |= c[rowID]
+
+        return ret
+
+    def setSegment(self, rowID, columnID, value = 1):
+        """Set value for a segment (default 1)"""
+        r = self.rows.get(rowID)
+        if r:
+            r[columnID] = 1
+
+        c = self.columns.get(columnID)
+        if c:
+            c[rowID] = 1
+
+    def getColumn(self, id):
+        return self.columns[id]
+
+    def mergeColumn(self, id, column):
+        self.columns[id] |= column
+        for xid, line in self.rows.items():
+            line[id] |= self.columns[id][xid]
+
+    def repairColumn(self, id):
+        success = self.columns[id].count(1)
+        if success >= self.blockSize/2:
+            ret = ~self.columns[id]
+            self.columns[id].setall(1)
+        else:
+            ret = zeros(self.blockSize)
+        return ret
+
+    def getRow(self, id):
+        return self.rows[id]
+
+    def mergeRow(self, id, row):
+        self.rows[id] |= row
+        for xid, line in self.columns.items():
+            line[id] |= self.rows[id][xid]
+
+    def repairRow(self, id):
+        success = self.rows[id].count(1)
+        if success >= self.blockSize/2:
+            ret = ~self.rows[id]
+            self.rows[id].setall(1)
+        else:
+            ret = zeros(self.blockSize)
+        return ret
+
+    # def print(self):
+    #     dash = "-" * (self.blockSize+2)
+    #     print(dash)
+    #     for i in range(self.blockSize):
+    #         line = "|"
+    #         for j in range(self.blockSize):
+    #             line += "%i" % self.data[(i*self.blockSize)+j]
+    #         print(line+"|")
+    #     print(dash)
+
diff --git a/DAS/validator.py b/DAS/validator.py
index b15d275..cb1be6c 100644
--- a/DAS/validator.py
+++ b/DAS/validator.py
@@ -49,8 +49,6 @@ class Validator:
         FORMAT = "%(levelname)s : %(entity)s : %(message)s"
         self.ID = ID
         self.format = {"entity": "Val "+str(self.ID)}
-        self.block = Block(self.shape.blockSize)
-        self.receivedBlock = Block(self.shape.blockSize)
         self.receivedQueue = deque()
         self.sendQueue = deque()
         self.amIproposer = amIproposer
@@ -73,6 +71,8 @@ class Validator:
                 self.columnIDs = columns if columns else unionOfSamples(range(self.shape.blockSize), self.shape.chi, self.vpn)
         self.rowNeighbors = collections.defaultdict(dict)
         self.columnNeighbors = collections.defaultdict(dict)
+        self.block = SparseBlock(shape.blockSize, self.rowIDs, self.columnIDs)
+        self.receivedBlock = SparseBlock(shape.blockSize, self.rowIDs, self.columnIDs)
 
         #statistics
         self.statsTxInSlot = 0