diff -r 46f59511b7bb -r d97fdabd9e2b src/HOL/Hahn_Banach/Subspace.thy
--- a/src/HOL/Hahn_Banach/Subspace.thy	Fri Sep 20 19:07:10 2024 +0200
+++ b/src/HOL/Hahn_Banach/Subspace.thy	Fri Sep 20 19:51:08 2024 +0200
@@ -23,7 +23,7 @@
     and mult_closed [iff]: "x \<in> U \<Longrightarrow> a \<cdot> x \<in> U"
 
 notation (symbols)
-  subspace  (infix "\<unlhd>" 50)
+  subspace  (infix \<open>\<unlhd>\<close> 50)
 
 declare vectorspace.intro [intro?] subspace.intro [intro?]