Allow several consecutive backs

Transition.py

@@ -18,8 +18,6 @@ class Transition :
 
   def apply(self, config, strategy) :
     data = None
-    
-    config.historyHistory.add(str([t[0].name for t in config.historyPop]))
 
     if self.name == "RIGHT" :
       applyRight(config)
@@ -32,6 +30,7 @@ class Transition :
     elif self.name == "EOS" :
       applyEOS(config)
     elif "BACK" in self.name :
+      config.historyHistory.add(str([t[0].name for t in config.historyPop]))
       size = int(self.name.split()[-1])
       applyBack(config, strategy, size)
     else :