diff -r 5c8177fd1295 -r 8e6c973003c8 src/Pure/Thy/export_theory.ML
--- a/src/Pure/Thy/export_theory.ML	Wed Oct 20 17:11:46 2021 +0200
+++ b/src/Pure/Thy/export_theory.ML	Wed Oct 20 18:13:17 2021 +0200
@@ -22,7 +22,6 @@
 (
   type T = (theory -> Name_Space.T) Inttab.table;
   val empty = Inttab.empty;
-  val extend = I;
   val merge = Inttab.merge (K true);
 );