diff --git a/notebooks/chap11.ipynb b/notebooks/chap11.ipynb
index 69acfd4..a0297ab 100644
--- a/notebooks/chap11.ipynb
+++ b/notebooks/chap11.ipynb
@@ -317,7 +317,6 @@
     "    def step(self):\n",
     "        \"\"\"Simulate a time step and update the instruments.\n",
     "        \"\"\"\n",
-    "        n = len(self.agents)\n",
     "        fits = self.get_fitnesses()\n",
     "        \n",
     "        # see who dies\n",