--- a/thys/PositionsExt.thy	Tue Oct 10 11:31:47 2017 +0100
+++ b/thys/PositionsExt.thy	Wed Oct 25 12:18:44 2017 +0100
@@ -1142,7 +1142,9 @@
 prefer 2
 apply(simp add: acyclic_def)
 apply(induct_tac rule: trancl.induct)
-apply(auto)[1]
+     apply(auto)[1]
+    prefer 3
+
 oops