diff --git a/ipynb/Advent of Code.ipynb b/ipynb/Advent of Code.ipynb
index 7af2248..812fe73 100644
--- a/ipynb/Advent of Code.ipynb	
+++ b/ipynb/Advent of Code.ipynb	
@@ -99,7 +99,7 @@
     "    \"The eight neighbors (with diagonals).\"\n",
     "    x, y = point \n",
     "    return ((x+1, y), (x-1, y), (x, y+1), (x, y-1),\n",
-    "            (X+1, y+1), (x-1, y-1), (x+1, y-1), (x-1, y+1))\n",
+    "            (x+1, y+1), (x-1, y-1), (x+1, y-1), (x-1, y+1))\n",
     "\n",
     "def cityblock_distance(p, q=(0, 0)): \n",
     "    \"City block distance between two points.\"\n",