adapt Refute example to reflect latest soundness fix to Refute

--- a/src/HOL/ex/Refute_Examples.thy	Tue Apr 13 15:16:54 2010 +0200
+++ b/src/HOL/ex/Refute_Examples.thy	Tue Apr 13 15:30:15 2010 +0200
@@ -1361,7 +1361,8 @@
 | "x : a_odd \<Longrightarrow> f x : a_even"
 
 lemma "x : a_odd"
-  refute  -- {* finds a model of size 2, as expected *}
+  (* refute  -- {* finds a model of size 2, as expected *}
+     NO LONGER WORKS since "lfp"'s interpreter is disabled *)
 oops
 
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