diff --git a/birch.py b/birch.py
index b3ec33b..b842541 100644
--- a/birch.py
+++ b/birch.py
@@ -93,6 +93,7 @@ def d0(self,other):
     
     def d2(self,other):
         # print "\n\nself%s %s\nn: %i other n: %i" % (hash(self), self, self.n,other.n)
+        # i really can't understand what the '%' here means, can you explain that, thanks.
         return (other.n * self.squared + self.n * other.squared - 2 * (self.ls % other.ls)) / (self.n * other.n)
     
     def d4(self,other):
@@ -528,7 +529,7 @@ def length(self):
     @property
     def squared(self):
         if not self._squared:
-            self._squared = self % self
+            self._squared = self.__mod__(self, self) # maybe here needs dot production
         return self._squared
     
     def distance(self,other):
@@ -602,4 +603,4 @@ def distance(self,other):
     
     time = datetime.now()-start # Stop measuring the computing time
     print "took %s (%.2fms per point)" % (time,(time.seconds*1000+time.microseconds/1000.0)/totalpoints)
-    print "splitcount: %s, nodecount: %s, entrycount: %s, leafcount: %s" % (splitcount, nodecount, entrycount, leafcount)
\ No newline at end of file
+    print "splitcount: %s, nodecount: %s, entrycount: %s, leafcount: %s" % (splitcount, nodecount, entrycount, leafcount)