src/Pure/Thy/sessions.scala

--- a/src/Pure/Thy/sessions.scala	Mon Nov 16 23:17:16 2020 +0100
+++ b/src/Pure/Thy/sessions.scala	Mon Nov 16 23:19:07 2020 +0100
@@ -814,7 +814,7 @@
         })
 
     def session_chapters: List[(String, String)] =
-      build_topological_order.map(name => name -> apply(name).chapter)
+      imports_topological_order.map(name => name -> apply(name).chapter)
 
     override def toString: String =
       imports_graph.keys_iterator.mkString("Sessions.Structure(", ", ", ")")