With the above SVN project checked out, run the resident compiler in the project's src/lampion/collections direc\
tory. In the same resident session, compile PriorityTree.scala first, then compile Test.scala, you should get th\
e following crash:

nsc> PriorityTree.scala

nsc> Test.scala
Exception in thread "main" java.lang.Error: key not found: trait BasicTreeNode$class
        at scala.Predef$.error(Predef.scala:155)
        at scala.collection.Map$class.default(Map.scala:184)
        at scala.collection.mutable.HashMap.default(HashMap.scala:21)
        at scala.collection.Map$class.apply(Map.scala:62)
        at scala.collection.mutable.HashMap.apply(HashMap.scala:21)
        at scala.tools.nsc.transform.OverridingPairs$Cursor.hasCommonParent(OverridingPairs.scala:82)
        at scala.tools.nsc.transform.OverridingPairs$Cursor.next(OverridingPairs.scala:106)
        at scala.tools.nsc.transform.OverridingPairs$Cursor.next(OverridingPairs.scala:119)
        at scala.tools.nsc.transform.OverridingPairs$Cursor.next(OverridingPairs.scala:119)
        at scala.tools.nsc.transform.OverridingPairs$Cursor.next(OverridingPairs.scala:119)
        at scala.tools.nsc.transform.OverridingPairs$Cursor.next(OverridingPairs.scala:119)
        at scala.tools.nsc.transform.OverridingPairs$Cursor.next(OverridingPairs.scala:119)
        at scala.tools.nsc.transform.OverridingPairs$Cursor.next(OverridingPairs.scala:119)
        at scala.tools.nsc.transform.OverridingPairs$Cursor.next(OverridingPairs.scala:119)
        at scala.tools.nsc.transform.OverridingPairs$Cursor.next(OverridingPairs.scala:119)
        at scala.tools.nsc.transform.OverridingPairs$Cursor.next(OverridingPairs.scala:119)
        at scala.tools.nsc.transform.OverridingPairs$Cursor.next(OverridingPairs.scala:119)
        at scala.tools.nsc.transform.OverridingPairs$Cursor.next(OverridingPairs.scala:119)
        at scala.tools.nsc.transform.OverridingPairs$Cursor.next(OverridingPairs.scala:119)
        at scala.tools.nsc.transform.OverridingPairs$Cursor.next(OverridingPairs.scala:119)
        at scala.tools.nsc.transform.OverridingPairs$Cursor.next(OverridingPairs.scala:119)
        at scala.tools.nsc.transform.OverridingPairs$Cursor.next(OverridingPairs.scala:119)
        at scala.tools.nsc.transform.OverridingPairs$Cursor.next(OverridingPairs.scala:119)
        at scala.tools.nsc.transform.OverridingPairs$Cursor.next(OverridingPairs.scala:119)
        at scala.tools.nsc.transform.OverridingPairs$Cursor.next(OverridingPairs.scala:119)
        at scala.tools.nsc.transform.OverridingPairs$Cursor.next(OverridingPairs.scala:119)
        at scala.tools.nsc.transform.OverridingPairs$Cursor.next(OverridingPairs.scala:119)
        at scala.tools.nsc.transform.OverridingPairs$Cursor.next(OverridingPairs.scala:119)
        at scala.tools.nsc.transform.OverridingPairs$Cursor.next(OverridingPairs.scala:119)
        at scala.tools.nsc.typechecker.RefChecks$RefCheckTransformer.checkAllOverrides(RefChecks.scala:207)
        at scala.tools.nsc.typechecker.RefChecks$RefCheckTransformer.transform(RefChecks.scala:553)
        at scala.tools.nsc.ast.Trees$Transformer.transformTemplate(Trees.scala:1024)
        at scala.tools.nsc.ast.Trees$Transformer$$anonfun$13.apply(Trees.scala:930)
        at scala.tools.nsc.ast.Trees$Transformer$$anonfun$13.apply(Trees.scala:930)
        at scala.tools.nsc.ast.Trees$Transformer.atOwner(Trees.scala:1044)
        at scala.tools.nsc.ast.Trees$Transformer.transform(Trees.scala:929)
        at scala.tools.nsc.typechecker.RefChecks$RefCheckTransformer.transform(RefChecks.scala:624)
        at scala.tools.nsc.typechecker.RefChecks$RefCheckTransformer.transformStat(RefChecks.scala:488)
        at scala.tools.nsc.typechecker.RefChecks$RefCheckTransformer$$anonfun$12.apply(RefChecks.scala:443)
        at scala.tools.nsc.typechecker.RefChecks$RefCheckTransformer$$anonfun$12.apply(RefChecks.scala:443)
        at scala.List.flatMap(List.scala:921)
        at scala.tools.nsc.typechecker.RefChecks$RefCheckTransformer.transformStats(RefChecks.scala:443)
        at scala.tools.nsc.ast.Trees$Transformer.transform(Trees.scala:962)
        at scala.tools.nsc.typechecker.RefChecks$RefCheckTransformer.transform(RefChecks.scala:624)
        at scala.tools.nsc.ast.Trees$Transformer.transformTemplate(Trees.scala:1024)
        at scala.tools.nsc.ast.Trees$Transformer$$anonfun$13.apply(Trees.scala:930)
        at scala.tools.nsc.ast.Trees$Transformer$$anonfun$13.apply(Trees.scala:930)
        at scala.tools.nsc.ast.Trees$Transformer.atOwner(Trees.scala:1044)
        at scala.tools.nsc.ast.Trees$Transformer.transform(Trees.scala:929)
        at scala.tools.nsc.typechecker.RefChecks$RefCheckTransformer.transform(RefChecks.scala:624)
        at scala.tools.nsc.typechecker.RefChecks$RefCheckTransformer.transformStat(RefChecks.scala:488)
        at scala.tools.nsc.typechecker.RefChecks$RefCheckTransformer$$anonfun$12.apply(RefChecks.scala:443)
        at scala.tools.nsc.typechecker.RefChecks$RefCheckTransformer$$anonfun$12.apply(RefChecks.scala:443)
        at scala.List.flatMap(List.scala:921)
        at scala.tools.nsc.typechecker.RefChecks$RefCheckTransformer.transformStats(RefChecks.scala:443)
        at scala.tools.nsc.ast.Trees$Transformer$$anonfun$12.apply(Trees.scala:926)
        at scala.tools.nsc.ast.Trees$Transformer$$anonfun$12.apply(Trees.scala:926)
        at scala.tools.nsc.ast.Trees$Transformer.atOwner(Trees.scala:1044)
        at scala.tools.nsc.ast.Trees$Transformer.transform(Trees.scala:925)
        at scala.tools.nsc.typechecker.RefChecks$RefCheckTransformer.transform(RefChecks.scala:624)
        at scala.tools.nsc.typechecker.RefChecks$RefCheckTransformer.transformStat(RefChecks.scala:488)
        at scala.tools.nsc.typechecker.RefChecks$RefCheckTransformer$$anonfun$12.apply(RefChecks.scala:443)
        at scala.tools.nsc.typechecker.RefChecks$RefCheckTransformer$$anonfun$12.apply(RefChecks.scala:443)
        at scala.List.flatMap(List.scala:921)
        at scala.tools.nsc.typechecker.RefChecks$RefCheckTransformer.transformStats(RefChecks.scala:443)
        at scala.tools.nsc.ast.Trees$Transformer$$anonfun$12.apply(Trees.scala:926)
        at scala.tools.nsc.ast.Trees$Transformer$$anonfun$12.apply(Trees.scala:926)
        at scala.tools.nsc.ast.Trees$Transformer.atOwner(Trees.scala:1044)
        at scala.tools.nsc.ast.Trees$Transformer.transform(Trees.scala:925)
        at scala.tools.nsc.typechecker.RefChecks$RefCheckTransformer.transform(RefChecks.scala:624)
        at scala.tools.nsc.ast.Trees$Transformer.transformUnit(Trees.scala:1039)
        at scala.tools.nsc.transform.Transform$Phase.apply(Transform.scala:22)
        at scala.tools.nsc.Global$GlobalPhase.applyPhase(Global.scala:208)
        at scala.tools.nsc.Global$GlobalPhase$$anonfun$1.apply(Global.scala:197)
        at scala.tools.nsc.Global$GlobalPhase$$anonfun$1.apply(Global.scala:197)
        at scala.Iterator$class.foreach(Iterator.scala:277)
        at scala.collection.mutable.ListBuffer$$anon$0.foreach(ListBuffer.scala:216)
        at scala.tools.nsc.Global$GlobalPhase.run(Global.scala:197)
        at scala.tools.nsc.Global$Run.compileSources(Global.scala:422)
        at scala.tools.nsc.Global$Run.compile(Global.scala:480)
        at scala.tools.nsc.Main$$anonfun$0.apply(Main.scala:39)
        at scala.tools.nsc.Main$$anonfun$0.apply(Main.scala:36)
        at scala.tools.nsc.EvalLoop$class.loop(EvalLoop.scala:11)
        at scala.tools.nsc.Main$.loop(Main.scala:16)
        at scala.tools.nsc.EvalLoop$class.loop(EvalLoop.scala:12)
        at scala.tools.nsc.Main$.loop(Main.scala:16)
        at scala.tools.nsc.EvalLoop$class.loop(EvalLoop.scala:12)
        at scala.tools.nsc.Main$.loop(Main.scala:16)
        at scala.tools.nsc.Main$.resident(Main.scala:36)
        at scala.tools.nsc.Main$.process(Main.scala:55)
        at scala.tools.nsc.Main$.main(Main.scala:80)
        at scala.tools.nsc.Main.main(Main.scala)