diff -r e9ab4ad7bd15 -r 23307fd33906 src/Doc/Tutorial/Misc/Plus.thy
--- a/src/Doc/Tutorial/Misc/Plus.thy	Thu Jan 11 13:48:17 2018 +0100
+++ b/src/Doc/Tutorial/Misc/Plus.thy	Fri Jan 12 14:08:53 2018 +0100
@@ -2,13 +2,13 @@
 theory Plus imports Main begin
 (*>*)
 
-text{*\noindent Define the following addition function *}
+text\<open>\noindent Define the following addition function\<close>
 
 primrec add :: "nat \<Rightarrow> nat \<Rightarrow> nat" where
 "add m 0 = m" |
 "add m (Suc n) = add (Suc m) n"
 
-text{*\noindent and prove*}
+text\<open>\noindent and prove\<close>
 (*<*)
 lemma [simp]: "!m. add m n = m+n"
 apply(induct_tac n)