diff --git a/2023/day16.py b/2023/day16.py
index a007b63..b7bc19b 100644
--- a/2023/day16.py
+++ b/2023/day16.py
@@ -29,11 +29,11 @@ def simulate_light(grid, start, initial_d):
         if grid[photon] == '.':
             photons.append((photon + d, d))
         elif grid[photon] == '/':
-            nd = [W, E, S, N][[N, S, E, W].index(d)]
-            photons.append((photon + nd, nd))
+            # ~d takes N <-> E and S <-> W
+            photons.append((photon + ~d, ~d))
         elif grid[photon] == '\\':
-            nd = [E, W, N, S][[N, S, E, W].index(d)]
-            photons.append((photon + nd, nd))
+            # -~d takes N <-> W and S <-> E
+            photons.append((photon + -~d, -~d))
         elif grid[photon] == '|':
             if d in (N, S):
                 photons.append((photon + d, d))
diff --git a/2023/utils.py b/2023/utils.py
index 5b6441a..923307c 100644
--- a/2023/utils.py
+++ b/2023/utils.py
@@ -466,6 +466,9 @@ class Point:
     def __lt__(self, other):
         return self.length < other.length
 
+    def __invert__(self):
+        return Point(-self.y, -self.x)
+
     def __str__(self):
         return "({}, {})".format(self.x, self.y)