diff -r 46f59511b7bb -r d97fdabd9e2b src/HOL/Quotient_Examples/Quotient_Message.thy
--- a/src/HOL/Quotient_Examples/Quotient_Message.thy	Fri Sep 20 19:07:10 2024 +0200
+++ b/src/HOL/Quotient_Examples/Quotient_Message.thy	Fri Sep 20 19:51:08 2024 +0200
@@ -17,7 +17,7 @@
         | DECRYPT  nat freemsg
 
 inductive
-  msgrel::"freemsg \<Rightarrow> freemsg \<Rightarrow> bool" (infixl "\<sim>" 50)
+  msgrel::"freemsg \<Rightarrow> freemsg \<Rightarrow> bool" (infixl \<open>\<sim>\<close> 50)
 where
   CD:    "CRYPT K (DECRYPT K X) \<sim> X"
 | DC:    "DECRYPT K (CRYPT K X) \<sim> X"