1.1 --- a/src/HOL/Set.ML	Mon Oct 20 17:21:54 1997 +0200
     1.2 +++ b/src/HOL/Set.ML	Tue Oct 21 10:36:23 1997 +0200
     1.3 @@ -623,6 +623,10 @@
     1.4  by (Blast_tac 1);
     1.5  qed "image_Un";
     1.6  
     1.7 +goal Set.thy "(z : f``A) = (EX x:A. z = f x)";
     1.8 +by (Blast_tac 1);
     1.9 +qed "image_iff";
    1.10 +
    1.11  
    1.12  (*** Range of a function -- just a translation for image! ***)
    1.13