diff --git a/bisimulation_algorithms/dovier_piazza_policriti/graph_entities.py b/bisimulation_algorithms/dovier_piazza_policriti/graph_entities.py
index 62b3839..1e5563f 100644
--- a/bisimulation_algorithms/dovier_piazza_policriti/graph_entities.py
+++ b/bisimulation_algorithms/dovier_piazza_policriti/graph_entities.py
@@ -3,7 +3,7 @@
 from bisimulation_algorithms.paige_tarjan.graph_entities import (
     _Vertex as pta_Vertex,
     _QBlock as pta_Block,
-    _XBlock
+    _XBlock,
 )
 
 
@@ -26,6 +26,7 @@ def scale_label(self, scaled_label: int):
     def back_to_original_label(self):
         self.label = self.original_label
 
+
 class _Block(pta_Block):
     def __init__(self, vertexes: Iterable[_Vertex], xblock: _XBlock):
         super().__init__(vertexes, xblock)