diff --git a/lib/gpt/core/object_type/complex_additive_group.py b/lib/gpt/core/object_type/complex_additive_group.py
index f7889e91a..c01a155be 100644
--- a/lib/gpt/core/object_type/complex_additive_group.py
+++ b/lib/gpt/core/object_type/complex_additive_group.py
@@ -91,6 +91,9 @@ def __init__(self, n):
         }
         self.cache = {}
 
+    def infinitesimal_to_cartesian(self, a, da):
+        return da
+
     def compose(self, a, b):
         return a + b