diff --git a/core.agda b/core.agda
index e3565c6..133bf2c 100644
--- a/core.agda
+++ b/core.agda
@@ -284,7 +284,6 @@ module core where
     var   : Nat → shape
     lam   : Nat → shape
     ap    : shape
-    arg   : shape
     numlit : Nat → shape
     plus  : shape
     nehole : shape