diff -r 4b03e3586f7f -r 31781b2de73d src/HOL/Lattice/Lattice.thy
--- a/src/HOL/Lattice/Lattice.thy	Thu Jun 14 22:59:42 2007 +0200
+++ b/src/HOL/Lattice/Lattice.thy	Thu Jun 14 23:04:36 2007 +0200
@@ -232,7 +232,7 @@
   show "x \<sqsubseteq> x" ..
   show "x \<sqsubseteq> x \<squnion> y" ..
   fix z assume "z \<sqsubseteq> x" and "z \<sqsubseteq> x \<squnion> y"
-  show "z \<sqsubseteq> x" by assumption
+  show "z \<sqsubseteq> x" by fact
 qed
 
 theorem join_meet_absorb: "x \<squnion> (x \<sqinter> y) = x"