diff --git a/demo/DemoClassification.ipynb b/demo/DemoClassification.ipynb
index 4882e498..26bac02c 100644
--- a/demo/DemoClassification.ipynb
+++ b/demo/DemoClassification.ipynb
@@ -231,27 +231,24 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 15,
+   "execution_count": 9,
    "outputs": [
     {
      "name": "stdout",
      "output_type": "stream",
      "text": [
       "CART performance (3 rules):\n",
-      "Accuracy = 0.40\n",
-      "Fidelity = 0.39\n",
-      "\n"
-     ]
-    },
-    {
-     "ename": "TypeError",
-     "evalue": "can only concatenate str (not \"it.unibo.tuprolog.theory.impl.MutableIndexedTheory\") to str",
-     "output_type": "error",
-     "traceback": [
-      "\u001B[1;31m---------------------------------------------------------------------------\u001B[0m",
-      "\u001B[1;31mTypeError\u001B[0m                                 Traceback (most recent call last)",
-      "\u001B[1;32m~\\AppData\\Local\\Temp/ipykernel_12108/2184489703.py\u001B[0m in \u001B[0;36m<module>\u001B[1;34m\u001B[0m\n\u001B[0;32m      6\u001B[0m \u001B[0mprint\u001B[0m\u001B[1;33m(\u001B[0m\u001B[1;34mf'Fidelity = {cart.accuracy(test, predictor):.2f}\\n'\u001B[0m\u001B[1;33m)\u001B[0m\u001B[1;33m\u001B[0m\u001B[1;33m\u001B[0m\u001B[0m\n\u001B[0;32m      7\u001B[0m \u001B[1;31m#print('\\nCART extracted rules:\\n\\n' + pretty_theory(theory_from_cart))\u001B[0m\u001B[1;33m\u001B[0m\u001B[1;33m\u001B[0m\u001B[0m\n\u001B[1;32m----> 8\u001B[1;33m \u001B[0mprint\u001B[0m\u001B[1;33m(\u001B[0m\u001B[1;34m'\\nCART extracted rules:\\n\\n'\u001B[0m \u001B[1;33m+\u001B[0m \u001B[0mtheory_from_cart\u001B[0m\u001B[1;33m)\u001B[0m\u001B[1;33m\u001B[0m\u001B[1;33m\u001B[0m\u001B[0m\n\u001B[0m",
-      "\u001B[1;31mTypeError\u001B[0m: can only concatenate str (not \"it.unibo.tuprolog.theory.impl.MutableIndexedTheory\") to str"
+      "Accuracy = 0.95\n",
+      "Fidelity = 0.96\n",
+      "\n",
+      "\n",
+      "CART extracted rules:\n",
+      "\n",
+      "iris(PetalLength, PetalWidth, SepalLength, SepalWidth, setosa) :-\n",
+      "    PetalLength =< 2.35.\n",
+      "iris(PetalLength, PetalWidth, SepalLength, SepalWidth, versicolor) :-\n",
+      "    PetalWidth =< 1.75.\n",
+      "iris(PetalLength, PetalWidth, SepalLength, SepalWidth, virginica).\n"
      ]
     }
    ],
@@ -469,7 +466,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": null,
+   "execution_count": 12,
    "outputs": [],
    "source": [],
    "metadata": {