Fix introduction example

examples/IntroductionIntoPyNeuraLogic.ipynb

@@ -17,7 +17,7 @@
     "\n",
     "<sub>[1] i.e. the template here does not contain any variables, causing it to correspond to a standard neural network rather than a GNN.</sub>\n",
     "\n",
-    "The XOR operation has two inputs - $I_1 ∈ \\{0, 1\\}$ and $I_2 ∈ \\{0, 1\\}$, and one output $O ∈ \\{0, 1\\}$. The whole operation can be summarized by Table [1](#).\n",
+    "The XOR operation has two inputs - $I_1 \\in \\{0, 1\\}$ and $I_2 \\in \\{0, 1\\}$, and one output $O \\in \\{0, 1\\}$. The whole operation can be summarized by Table [1](#).\n",
     "\n",
     "#### Table 1: The XOR truth table\n",
     "| X | Y | O |\n",