From cfb17517eb3d3fefa2edced5529c15f7455e3800 Mon Sep 17 00:00:00 2001
From: Paul Romano <paul.k.romano@gmail.com>
Date: Mon, 5 Oct 2015 07:45:55 +0700
Subject: [PATCH] Overload __invert__ for Halfspace (return opposite Halfspace)

---
 openmc/surface.py | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/openmc/surface.py b/openmc/surface.py
index 66376c2a0c..afa426fa3b 100644
--- a/openmc/surface.py
+++ b/openmc/surface.py
@@ -988,6 +988,9 @@ class Halfspace(Region):
         self.surface = surface
         self.side = side
 
+    def __invert__(self):
+        return -self.surface if self.side == '+' else +self.surface
+
     @property
     def surface(self):
         return self._surface