diff --git a/README.md b/README.md
index 73ff2a1..9ec7b5b 100644
--- a/README.md
+++ b/README.md
@@ -30,6 +30,7 @@ This is nowhere near complete. Stay tuned.
 ## Internals
  - Copy expression
  - Non-recursive treeify
+ - Faster factorial function. Maybe use gamma instead?
 
 ## Features
  - Variable definitions