Cannot do BACK when back already happened for that word

Config.py

@@ -18,7 +18,7 @@ class Config :
     self.stack = []
     self.comments = []
     self.history = []
-    self.historyHistory = set()
+    self.backHistory = set()
     self.historyPop = []
 
   def isPredicted(self, colname) :

Transition.py

@@ -43,7 +43,7 @@ class Transition :
       data = None
       config.nbUndone = max(0, config.nbUndone-1)
     elif "BACK" in self.name :
-      config.historyHistory.add(str([t[0].name for t in config.historyPop]))
+      config.backHistory.add(config.wordIndex)
       applyBack(config, strategy, self.size)
     else :
       print("ERROR : nothing to apply for '%s'"%self.name, file=sys.stderr)
@@ -89,7 +89,7 @@ class Transition :
     if "BACK" in self.name :
       if len([h[0].name for h in config.historyPop if "NOBACK" in h[0].name]) < self.size :
         return False
-      return str([t[0].name for t in config.historyPop]) not in config.historyHistory
+      return config.wordIndex not in config.backHistory
 
     print("ERROR : appliable, unknown name '%s'"%self.name, file=sys.stderr)
     exit(1)