diff --git a/memonto/core/retain.py b/memonto/core/retain.py
index 16b819c..10c7da3 100644
--- a/memonto/core/retain.py
+++ b/memonto/core/retain.py
@@ -207,7 +207,7 @@ def _retain(
 ) -> None:
     str_ontology = ontology.serialize(format="turtle")
     updated_memory = ""
-    
+
     if auto_expand:
         ontology = expand_ontology(
             ontology=ontology,