diff -r 90abc28523d7 -r f8b1a75dbea7 src/Pure/Thy/sessions.scala
--- a/src/Pure/Thy/sessions.scala	Fri Dec 16 15:14:09 2022 +0100
+++ b/src/Pure/Thy/sessions.scala	Fri Dec 16 16:00:56 2022 +0100
@@ -792,8 +792,6 @@
   ) {
     sessions_structure =>
 
-    def bootstrap: Base = Base(overall_syntax = Thy_Header.bootstrap_syntax)
-
     def dest_session_directories: List[(String, String)] =
       for ((file, session) <- session_directories.toList)
         yield (File.standard_path(file), session)