diff -r b1e0fb71435d -r fdfe9b91d96e src/Pure/Tools/simplifier_trace.scala
--- a/src/Pure/Tools/simplifier_trace.scala	Tue Aug 29 12:04:13 2023 +0200
+++ b/src/Pure/Tools/simplifier_trace.scala	Tue Aug 29 12:53:28 2023 +0200
@@ -208,7 +208,7 @@
                       def purge(queue: Vector[Long]): Unit =
                         queue match {
                           case s +: rest =>
-                            for (Item(Markup.SIMP_TRACE_STEP, data) <- results.get(s))
+                            for (case Item(Markup.SIMP_TRACE_STEP, data) <- results.get(s))
                               memory -= Index.of_data(data)
                             val children = memory_children.getOrElse(s, Set.empty)
                             memory_children -= s