diff -r 713424d012fd -r 70076ba563d2 src/HOL/Auth/Message.thy
--- a/src/HOL/Auth/Message.thy	Wed Aug 28 20:46:45 2024 +0200
+++ b/src/HOL/Auth/Message.thy	Wed Aug 28 22:54:45 2024 +0200
@@ -49,10 +49,13 @@
 
 
 text\<open>Concrete syntax: messages appear as \<open>\<lbrace>A,B,NA\<rbrace>\<close>, etc...\<close>
+nonterminal mtuple_args
 syntax
-  "_MTuple" :: "['a, args] \<Rightarrow> 'a * 'b"  ("(2\<lbrace>_,/ _\<rbrace>)")
+  "" :: "'a \<Rightarrow> mtuple_args"  ("_")
+  "_MTuple_args" :: "'a \<Rightarrow> mtuple_args \<Rightarrow> mtuple_args"  ("_,/ _")
+  "_MTuple" :: "['a, mtuple_args] \<Rightarrow> 'a * 'b"  ("(2\<lbrace>_,/ _\<rbrace>)")
 syntax_consts
-  "_MTuple" \<rightleftharpoons> MPair
+  "_MTuple_args" "_MTuple" \<rightleftharpoons> MPair
 translations
   "\<lbrace>x, y, z\<rbrace>" \<rightleftharpoons> "\<lbrace>x, \<lbrace>y, z\<rbrace>\<rbrace>"
   "\<lbrace>x, y\<rbrace>" \<rightleftharpoons> "CONST MPair x y"