diff --git a/src/statebag.py b/src/statebag.py
--- a/src/statebag.py
+++ b/src/statebag.py
@@ -42,6 +42,7 @@ class GameTreeNode:
 	## Connect itself after v if it gains itself more weight.
 	def tryConnect(self,v,diff):
 		moves=getTransitionSequence(v.parent,self.parent,-1*v.color,self.color,diff)
+		if not moves: return
 		w=v.weight+2-len(moves) # proper one move transition increases the weight by 1
 		if w>self.weight:
 			self.moves=moves
@@ -57,10 +58,10 @@ class BoardState:
 		self._hash=None
 
 	def tryConnect(self,s):
-		diff=s-self
+		diff=self-s
 		distEst=estimateDistance(diff)
 		if distEst>3: return # we couldn't find every such move sequence anyway without a clever algorithm
-		weightEst=s.getWeight()-distEst
+		weightEst=s.getWeight()+2-distEst
 		if weightEst<=self.getWeight(): return
 		for v1 in s.nodes:
 			for v2 in self.nodes:
@@ -94,9 +95,16 @@ class BoardState:
 	def __eq__(self,x):
 		return self.hash()==x.hash()
 
+	def setWeight(self,val):
+		for v in self.nodes: v.weight=val
+
 	def getWeight(self):
 		return max(v.weight for v in self.nodes)
 
+	def getPrev(self):
+		v=max(self.nodes, key=lambda v: v.weight)
+		return v.prev.parent if v.prev else None
+
 
 class StateBag:
 	def __init__(self):
@@ -104,11 +112,15 @@ class StateBag:
 
 	def pushState(self,board):
 		sn=BoardState(board)
-		if self._states and sn==self._states[-1]: return # no change
+		if len(self._states)>0:
+			if sn==self._states[-1]: return None # no change
+			sn.diff2Prev=sn-self._states[-1]
+		else: sn.setWeight(1)
 
 		for s in reversed(self._states):
 			sn.tryConnect(s)
 		self._states.append(sn)
+		return sn
 
 	def merge(self,branch):
 		pass