diff --git a/steffen-schuldenzucker.md b/steffen-schuldenzucker.md
index b526d4a4a..3e53111cc 100644
--- a/steffen-schuldenzucker.md
+++ b/steffen-schuldenzucker.md
@@ -25,6 +25,9 @@
   - [[rotations]]?
   - [[meet scaling]]
 - [[jonathan the utopian]]
+  - [[category theory]]
+    - [[steffen]] did some during earlier studies -- perhaps it was too early. Later in studies it came very handy.
+    - also used it in [[haskell]]
 
 
 [//begin]: # "Autogenerated link references for markdown compatibility"