diff --git a/module3/exo3/exercice.ipynb b/module3/exo3/exercice.ipynb
index 1fd533de0c053d1872e2231958377ac10b33e051..ba55b3976059b5976aee25dc9368c991c85433f8 100644
--- a/module3/exo3/exercice.ipynb
+++ b/module3/exo3/exercice.ipynb
@@ -56,6 +56,7 @@
     }
    ],
    "source": [
+    "# Install library/package\n",
     "pip install arviz"
    ]
   },
@@ -81,6 +82,7 @@
     }
    ],
    "source": [
+    "# Install library/package\n",
     "pip install git+https://github.com/pymc-devs/pymc3"
    ]
   },
@@ -108,6 +110,7 @@
     }
    ],
    "source": [
+    "# Install library/package\n",
     "pip install bokeh"
    ]
   },
@@ -127,6 +130,7 @@
     }
    ],
    "source": [
+    "# Install library/package\n",
     "conda create -n py35 python=3.5 anaconda"
    ]
   },
@@ -146,25 +150,17 @@
     }
    ],
    "source": [
+    "# Install library/package\n",
     "conda install spyder"
    ]
   },
   {
    "cell_type": "code",
-   "execution_count": 4,
+   "execution_count": 9,
    "metadata": {},
-   "outputs": [
-    {
-     "name": "stdout",
-     "output_type": "stream",
-     "text": [
-      "Collecting package metadata (current_repodata.json): | Killed\n",
-      "\n",
-      "Note: you may need to restart the kernel to use updated packages.\n"
-     ]
-    }
-   ],
+   "outputs": [],
    "source": [
+    "# Install library/package\n",
     "conda install theano"
    ]
   },
@@ -184,6 +180,7 @@
     }
    ],
    "source": [
+    "# Install library/package\n",
     "conda install tensorflow"
    ]
   },
@@ -203,6 +200,7 @@
     }
    ],
    "source": [
+    "# Install library/package\n",
     "conda install keras"
    ]
   },
@@ -265,6 +263,7 @@
     }
    ],
    "source": [
+    "# Install library/package\n",
     "pip install pymc3"
    ]
   },
@@ -291,6 +290,7 @@
     }
    ],
    "source": [
+    "# Install library/package\n",
     "pip install numpy==1.15.4"
    ]
   },
@@ -300,6 +300,7 @@
    "metadata": {},
    "outputs": [],
    "source": [
+    "# import library\n",
     "import numpy as np\n",
     "import pandas as pd\n",
     "import matplotlib.pyplot as plt"
@@ -528,6 +529,7 @@
     }
    ],
    "source": [
+    "# read dataset from URL (July 2021)\n",
     "data_url = \"https://scrippsco2.ucsd.edu/assets/data/atmospheric/stations/in_situ_co2/monthly/monthly_in_situ_co2_mlo.csv\"\n",
     "data_monthly= pd.read_csv(data_url,skiprows=54)\n",
     "data_monthly"
@@ -756,6 +758,7 @@
     }
    ],
    "source": [
+    "# Delete row 1:  first two lines : \" \" and “Excel”. These lines seems to be useless.\n",
     "data_monthly = data_monthly.iloc[1:]\n",
     "data_monthly"
    ]
@@ -983,6 +986,7 @@
     }
    ],
    "source": [
+    "# Delete row 1:  first two lines : \" \" and “Excel”. These lines seems to be useless.\n",
     "data = data_monthly.iloc[1:]\n",
     "data"
    ]
@@ -1280,6 +1284,7 @@
     }
    ],
    "source": [
+    "# Install library/package\n",
     "conda install mkl-service"
    ]
   },
@@ -1299,6 +1304,7 @@
     }
    ],
    "source": [
+    "# Install library/package\n",
     "pip install pymc3==3.11.2"
    ]
   },
@@ -1322,6 +1328,8 @@
     }
    ],
    "source": [
+    "# make plot\n",
+    "\n",
     "import pymc3 as pm\n",
     "import arviz as az\n",
     "import matplotlib.pyplot as plt\n",
@@ -1489,6 +1497,8 @@
    "metadata": {},
    "outputs": [],
    "source": [
+    "# make plot using ggplot\n",
+    "\n",
     "%matplotlib inline\n",
     "from plotnine.data import mpg\n",
     "from plotnine import ggplot\n",