src/Pure/General/linear_set.scala

--- a/src/Pure/General/linear_set.scala	Wed Jan 07 18:09:11 2015 +0100
+++ b/src/Pure/General/linear_set.scala	Thu Jan 08 20:56:39 2015 +0100
@@ -122,7 +122,7 @@
   override def size: Int = if (isEmpty) 0 else nexts.size + 1
 
   def contains(elem: A): Boolean =
-    !isEmpty && (end.get == elem || nexts.isDefinedAt(elem))
+    nonEmpty && (end.get == elem || nexts.isDefinedAt(elem))
 
   private def make_iterator(from: Option[A]): Iterator[A] = new Iterator[A] {
     private var next_elem = from