diff --git a/example_two_car_lane_switch.py b/example_two_car_lane_switch.py
index 145a1ffceed13cfc0e14f0cd900dc3cf4288f1f1..5abe0de67554a89d630ab519e12ed5833ecbff70 100644
--- a/example_two_car_lane_switch.py
+++ b/example_two_car_lane_switch.py
@@ -69,7 +69,7 @@ if __name__ == "__main__":
     scenario.set_init(
         [
             [[10, 0, 0, 0.5],[10, 0, 0, 0.5]], 
-            [[0, -0.2, 0, 1.0],[0, 0.2, 0, 1.0]],
+            [[-0.5, -0.2, 0, 1.0],[0.5, 0.2, 0, 1.0]],
         ],
         [
             (VehicleMode.Normal, LaneMode.Lane1),
@@ -81,7 +81,7 @@ if __name__ == "__main__":
     traces = scenario.verify(40)
 
     fig = plt.figure()
-    fig = plot_tree(traces, 'car1', 1, [2], 'b', fig)
+    # fig = plot_tree(traces, 'car1', 1, [2], 'b', fig)
     fig = plot_tree(traces, 'car2', 1, [2], 'r', fig)
 
     plt.show()
diff --git a/ourtool/automaton/guard.py b/ourtool/automaton/guard.py
index ba20942086404e6e9a5e624cc07e845d6f97e0bf..0a80a3a20109d44ed15060665d3e44142604f49e 100644
--- a/ourtool/automaton/guard.py
+++ b/ourtool/automaton/guard.py
@@ -220,6 +220,11 @@ class GuardExpressionAst:
                 expr = astunparse.unparse(node)
                 expr = expr.strip('\n')
                 return expr
+        elif isinstance(node, ast.UnaryOp):
+            # If is UnaryOp, 
+            value = self._generate_z3_expression_node(node.operand)
+            if isinstance(node.op, ast.USub):
+                return -value
         else:
             # For other cases, we can return the expression directly
             expr = astunparse.unparse(node)
@@ -327,6 +332,12 @@ class GuardExpressionAst:
                 return True, root
         elif isinstance(root, ast.Constant):
             return root.value, root
+        elif isinstance(root, ast.UnaryOp):
+            if isinstance(root.op, ast.USub):
+                res, root.operand = self._evaluate_guard_disc(root.operand, agent, disc_var_dict, lane_map)
+            else:
+                raise ValueError(f'Node type {root} from {astunparse.unparse(root)} is not supported')
+            return True, root
         else:
             raise ValueError(f'Node type {root} from {astunparse.unparse(root)} is not supported')