diff -r 162abcd128a1 -r 8755cdbbf6b3 src/HOL/HOL.thy
--- a/src/HOL/HOL.thy	Fri Dec 05 17:16:22 1997 +0100
+++ b/src/HOL/HOL.thy	Fri Dec 05 17:19:38 1997 +0100
@@ -183,6 +183,7 @@
   Let_def       "Let s f == f(s)"
   o_def         "(f::'b=>'c) o g == (%(x::'a). f(g(x)))"
   if_def        "If P x y == @z::'a. (P=True --> z=x) & (P=False --> z=y)"
+  arbitrary_def "False ==> arbitrary == (@x. False)"
 
 
 end