src/Pure/Thy/present.scala

--- a/src/Pure/Thy/present.scala	Mon Oct 05 21:15:58 2020 +0200
+++ b/src/Pure/Thy/present.scala	Mon Oct 05 22:07:25 2020 +0200
@@ -36,8 +36,7 @@
 
   def update_chapter_index(browser_info: Path, chapter: String, new_sessions: List[(String, String)])
   {
-    val dir = browser_info + Path.basic(chapter)
-    Isabelle_System.make_directory(dir)
+    val dir = Isabelle_System.make_directory(browser_info + Path.basic(chapter))
 
     val sessions0 =
       try { read_sessions(dir) }