diff --git a/.gitignore b/.gitignore
index 1140406f..f94768ac 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,4 +1,5 @@
 .DS_Store
 lectures/_build
-*/.ipynb_checkpoints/
+.ipynb_checkpoints/
+.virtual_documents/
 _build/*
diff --git a/lectures/_static/lecture_specific/graphviz/graphviz_generation.ipynb b/lectures/_static/lecture_specific/graphviz/graphviz_generation.ipynb
index e9568364..03c74116 100644
--- a/lectures/_static/lecture_specific/graphviz/graphviz_generation.ipynb
+++ b/lectures/_static/lecture_specific/graphviz/graphviz_generation.ipynb
@@ -18,7 +18,7 @@
      "name": "stdout",
      "output_type": "stream",
      "text": [
-      "Requirement already satisfied: graphviz in /Users/humphreyyang/anaconda3/envs/quantecon/lib/python3.9/site-packages (0.20.1)\n"
+      "Requirement already satisfied: graphviz in /Users/mmcky/anaconda3/envs/quantecon/lib/python3.11/site-packages (0.20.3)\n"
      ]
     }
    ],
@@ -289,7 +289,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 8,
+   "execution_count": 3,
    "id": "2d1becb5-6593-49e2-990f-e6a8799b7c2c",
    "metadata": {},
    "outputs": [
@@ -299,7 +299,7 @@
        "'../markov_chains_II/example4.png'"
       ]
      },
-     "execution_count": 8,
+     "execution_count": 3,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -310,8 +310,8 @@
     "dot.node(\"0\")\n",
     "dot.node(\"1\")\n",
     "\n",
-    "dot.edge(\"0\", \"1\", label=\"1.0\", color='red')\n",
-    "dot.edge(\"1\", \"0\", label=\"1.0\", color='red')\n",
+    "dot.edge(\"0\", \"1\", label=\"1.0\")\n",
+    "dot.edge(\"1\", \"0\", label=\"1.0\")\n",
     "\n",
     "dot\n",
     "dot.render(filename='../markov_chains_II/example4')"
@@ -557,7 +557,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.9.16"
+   "version": "3.11.7"
   }
  },
  "nbformat": 4,
diff --git a/lectures/_static/lecture_specific/markov_chains_II/example4.png b/lectures/_static/lecture_specific/markov_chains_II/example4.png
index 28902276..a7844b4b 100644
Binary files a/lectures/_static/lecture_specific/markov_chains_II/example4.png and b/lectures/_static/lecture_specific/markov_chains_II/example4.png differ