diff -r 46f59511b7bb -r d97fdabd9e2b src/HOL/Library/Extended_Nat.thy
--- a/src/HOL/Library/Extended_Nat.thy	Fri Sep 20 19:07:10 2024 +0200
+++ b/src/HOL/Library/Extended_Nat.thy	Fri Sep 20 19:51:08 2024 +0200
@@ -10,7 +10,7 @@
 begin
 
 class infinity =
-  fixes infinity :: "'a"  ("\<infinity>")
+  fixes infinity :: "'a"  (\<open>\<infinity>\<close>)
 
 context
   fixes f :: "nat \<Rightarrow> 'a::{canonically_ordered_monoid_add, linorder_topology, complete_linorder}"