diff --git a/.github/workflows/python-app.yml b/.github/workflows/python-app.yml
index 520892d..03a3c2d 100644
--- a/.github/workflows/python-app.yml
+++ b/.github/workflows/python-app.yml
@@ -31,20 +31,16 @@ jobs:
     name: Check code style
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v2
-    - name: Set up Python 3.8
-      uses: actions/setup-python@v2
+    - uses: actions/checkout@v4
+    - name: Set up Python 3.11
+      uses: actions/setup-python@v4
       with:
-        python-version: 3.8
+        python-version: 3.11
     - name: Install dependencies
       run: |
-        pip install flake8 pydocstyle
-    - name: Lint with flake8
+        python -m pip install --upgrade pip
+        pip install ruff
+    - name: Lint with ruff
       run: |
-        # stop the build if there are Python syntax errors or undefined names
-        flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics
-        # exit-zero treats all errors as warnings. The GitHub editor is 127 chars wide
-        flake8 . --count --max-complexity=10 --max-line-length=80 --statistics
-    - name: Check doc style with pydocstyle
-      run: pydocstyle
+         ruff check --output-format=github .
 
diff --git a/README.md b/README.md
index 823291d..d9f6cea 100644
--- a/README.md
+++ b/README.md
@@ -15,7 +15,7 @@
   - Create a branch called `my_user_name` using `git checkout -b my_user_name`
   - Make the changes to complete the assignment. You have to modify the files that contain `questions` in their name. Do not modify the files that start with `test_`.
   - Check locally that your solution meet the test by running `pytest` from the root of the repo. You may need to install `pytest` using `pip` or `conda`.
-  - Check the code formating for your solution using `flake8`. You may need to install `flake8` using `pip` or `conda`.
+  - Check the code formating for your solution using `ruff`. You may need to install `ruff` using `pip` or `conda`.
   - Open the pull request on GitHub:
      - Create a commit with `git add -u` and `git commit -m "UP my solution"`
      - Push your branch on your fork: `git push -u origin my_user_name`
diff --git a/numpy_questions.py b/numpy_questions.py
index 07a10c1..25674ee 100644
--- a/numpy_questions.py
+++ b/numpy_questions.py
@@ -15,6 +15,7 @@
 This will be enforced with `flake8`. You can check that there is no flake8
 errors by calling `flake8` at the root of the repo.
 """
+
 import numpy as np
 
 
@@ -39,9 +40,11 @@ def max_index(X):
     """
     i = 0
     j = 0
-
+    if not isinstance(X, np.ndarray) or X.ndim != 2:
+        raise ValueError()
     # TODO
-
+    max_val = np.max(X)
+    i, j = np.where(X == max_val)
     return i, j
 
 
@@ -64,4 +67,15 @@ def wallis_product(n_terms):
     """
     # XXX : The n_terms is an int that corresponds to the number of
     # terms in the product. For example 10000.
-    return 0.
+    if n_terms == 0:
+        return 2
+
+    product = 1
+    for i in range(1, n_terms + 1):
+        product *= (4 * i**2) / (4 * i**2 - 1)
+        
+        
+        
+        
+        
+    return 2 * product