diff --git a/src/gemseo/algos/problem_function.py b/src/gemseo/algos/problem_function.py
index 2f060612233ab36dbc2f17107f2fb9b4e171d7c6..38c00cc0fd032437c8c545a00fd49ad9113bce16 100644
--- a/src/gemseo/algos/problem_function.py
+++ b/src/gemseo/algos/problem_function.py
@@ -206,6 +206,10 @@ class ProblemFunction(MDOFunction, Serializable):
         Returns:
             The output value.
         """
+        # The lines below implement function compositions using a for-loop.
+        # For instance, unnormalize ``input_value``, then evaluate the original
+        # ``MDOFunction``. The output value of a function becomes the input value of
+        # the next function.
         for func in self._output_evaluation_sequence:
             input_value = func(input_value)
 
@@ -220,6 +224,10 @@ class ProblemFunction(MDOFunction, Serializable):
         Returns:
             The Jacobian.
         """
+        # The lines below implement function compositions using a for-loop.
+        # For instance, unnormalize ``input_value``, then evaluate the original
+        # ``MDOFunction``. The output value of a function becomes the input value of
+        # the next function.
         for func in self._jacobian_evaluation_sequence:
             input_value = func(input_value)