diff -r 524ba83940c2 -r 7ca11a7ace41 src/HOL/Set.thy
--- a/src/HOL/Set.thy	Wed Jun 28 16:01:34 2023 +0200
+++ b/src/HOL/Set.thy	Fri Jun 30 08:17:27 2023 +0200
@@ -774,7 +774,7 @@
     using that by (auto split: if_splits)
 qed
 
-lemma insert_UNIV: "insert x UNIV = UNIV"
+lemma insert_UNIV[simp]: "insert x UNIV = UNIV"
   by auto