diff -r d1523393dd5a -r 69c78980c8a4 ProgTutorial/Intro.thy
--- a/ProgTutorial/Intro.thy	Thu May 23 00:58:11 2019 +0100
+++ b/ProgTutorial/Intro.thy	Tue Jun 11 23:31:09 2019 +0100
@@ -29,7 +29,7 @@
   The best way to get to know the Isabelle/ML is by experimenting
   with the many code examples included in the tutorial. The code is as far as
   possible checked against the Isabelle
-  distribution.%%\footnote{\input{version.tex}}
+  distribution. %%\footnote{\input{version.tex}}
   If something does not work, then
   please let us know. It is impossible for us to know every environment,
   operating system or editor in which Isabelle is used. If you have comments,
@@ -51,8 +51,13 @@
   based on jEdit. This part of the code is beyond the interest of this
   tutorial, since it mostly does not concern the regular Isabelle 
   developer.
+\<close>
 
-  The rich Isabelle infrastructure can be categorized by various aspects @{cite "wenzel-technology"}:
+section \<open>Isabelle Infrastructure\<close>
+
+text \<open>
+There is a rich Isabelle infrastructure---it might be good to have the  following
+rough mind map @{cite "wenzel-technology"}:
 
      @{emph \<open>@{bold \<open>Logic\<close>}\<close>} 
       \begin{description}