diff --git a/.github/workflows/build_and_test.yaml b/.github/workflows/build_and_test.yaml
index 7e82bb8..be46942 100644
--- a/.github/workflows/build_and_test.yaml
+++ b/.github/workflows/build_and_test.yaml
@@ -11,10 +11,11 @@ jobs:
         python-version: ['3.9', '3.10']
 
     steps:
-    - uses: actions/checkout@v2
+    - name: Checkout code
+      uses: actions/checkout@v4
 
     - name: Set up Python ${{ matrix.python-version }}
-      uses: actions/setup-python@v2
+      uses: actions/setup-python@v5
       with:
         python-version: ${{ matrix.python-version }}
 
diff --git a/logicalinduction/formula.py b/logicalinduction/formula.py
index 1c08a2c..d208e5a 100644
--- a/logicalinduction/formula.py
+++ b/logicalinduction/formula.py
@@ -15,6 +15,8 @@ def __mul__(self, Number) -> 'Number':
         ...
     def __add__(self, Number) -> 'Number':
         ...
+    def __radd__(self, Number) -> 'Number':
+        ...
     def __lt__(self, Number) -> bool:
         ...
     def __gt__(self, Number) -> bool: