diff -r 539cc471186f -r 111d801b5d5d src/HOL/ATP.thy
--- a/src/HOL/ATP.thy	Sat Sep 20 10:44:24 2014 +0200
+++ b/src/HOL/ATP.thy	Sat Sep 20 10:44:24 2014 +0200
@@ -138,7 +138,7 @@
   by simp
 
 lemma boolean_comm: "(P \<longleftrightarrow> Q) = (Q \<longleftrightarrow> P)"
-  by metis
+  by auto
 
 lemmas waldmeister_fol = boolean_equality boolean_comm
   simp_thms(1-5,7-8,11-25,27-33) disj_comms disj_assoc conj_comms conj_assoc