--- a/src/HOL/Library/Extended.thy	Fri Sep 20 19:07:10 2024 +0200
+++ b/src/HOL/Library/Extended.thy	Fri Sep 20 19:51:08 2024 +0200
@@ -8,7 +8,7 @@
   imports Simps_Case_Conv
 begin
 
-datatype 'a extended = Fin 'a | Pinf ("\<infinity>") | Minf ("-\<infinity>")
+datatype 'a extended = Fin 'a | Pinf (\<open>\<infinity>\<close>) | Minf (\<open>-\<infinity>\<close>)
 
 
 instantiation extended :: (order)order