diff -r fd6e64133684 -r c115e69f457f src/Pure/PIDE/prover.scala
--- a/src/Pure/PIDE/prover.scala	Tue Mar 08 11:18:21 2016 +0100
+++ b/src/Pure/PIDE/prover.scala	Tue Mar 08 14:44:11 2016 +0100
@@ -39,6 +39,7 @@
   /* messages */
 
   sealed abstract class Message
+  type Receiver = Message => Unit
 
   class Input(val name: String, val args: List[String]) extends Message
   {
@@ -85,7 +86,7 @@
 
 
 abstract class Prover(
-  receiver: Prover.Message => Unit,
+  receiver: Prover.Receiver,
   system_channel: System_Channel,
   system_process: Prover.System_Process) extends Protocol
 {