--- a/src/Pure/Thy/presentation.scala Wed Nov 03 20:45:02 2021 +0100
+++ b/src/Pure/Thy/presentation.scala Wed Nov 03 20:53:52 2021 +0100
@@ -266,7 +266,7 @@
<center>
<table width="100%" border="0" cellspacing="10" cellpadding="0">
<tr>
- <td width="20%" valign="middle" align="center"><a href="http://isabelle.in.tum.de/"><img align="bottom" src="isabelle.gif" width="100" height="86" alt="[Isabelle]" border="0" /></a></td>
+ <td width="20%" valign="middle" align="center"><a href="https://isabelle.in.tum.de/"><img align="bottom" src="isabelle.gif" width="100" height="86" alt="[Isabelle]" border="0" /></a></td>
<td width="80%" valign="middle" align="center">
<table width="90%" border="0" cellspacing="0" cellpadding="20">