Add missing pickle import

examples/pysr_demo.ipynb

@@ -1302,7 +1302,7 @@
       "cell_type": "markdown",
       "metadata": {},
       "source": [
-        "We can now load the data:"
+        "We can now load the data, including after a crash (be sure to re-run the import cells at the top of this notebook, including the one that starts PyJulia)."
       ]
     },
     {
@@ -1311,6 +1311,8 @@
       "metadata": {},
       "outputs": [],
       "source": [
+        "import pickle as pkl\n",
+        "\n",
         "nnet_recordings = pkl.load(open(\"nnet_recordings.pkl\", \"rb\"))\n",
         "f_input = nnet_recordings[\"f_input\"]\n",
         "f_output = nnet_recordings[\"f_output\"]\n",