src/Pure/PIDE/prover.scala

--- a/src/Pure/PIDE/prover.scala	Tue Mar 05 16:40:12 2019 +0100
+++ b/src/Pure/PIDE/prover.scala	Tue Mar 05 18:44:02 2019 +0100
@@ -23,7 +23,7 @@
     override def toString: String =
       XML.Elem(Markup(Markup.PROVER_COMMAND, List((Markup.NAME, name))),
         args.map(s =>
-          List(XML.Text("\n"), XML.elem(Markup.PROVER_ARG, YXML.parse_body(s)))).flatten).toString
+          List(XML.newline, XML.elem(Markup.PROVER_ARG, YXML.parse_body(s)))).flatten).toString
   }
 
   class Output(val message: XML.Elem) extends Message