diff -r 1e31ddcab458 -r 4c275405faae src/Doc/Tutorial/Advanced/simp2.thy
--- a/src/Doc/Tutorial/Advanced/simp2.thy	Sun Jan 15 16:28:03 2023 +0100
+++ b/src/Doc/Tutorial/Advanced/simp2.thy	Sun Jan 15 18:30:18 2023 +0100
@@ -122,7 +122,7 @@
 rewrite rules. This is not quite true.  For reasons of feasibility,
 the simplifier expects the
 left-hand side of each rule to be a so-called \emph{higher-order
-pattern}~@{cite "nipkow-patterns"}\indexbold{patterns!higher-order}. 
+pattern}~\<^cite>\<open>"nipkow-patterns"\<close>\indexbold{patterns!higher-order}. 
 This restricts where
 unknowns may occur.  Higher-order patterns are terms in $\beta$-normal
 form.  (This means there are no subterms of the form $(\lambda x. M)(N)$.)