fixed overloading of "image"

--- a/src/HOL/Set.ML	Wed Aug 19 10:27:00 1998 +0200
+++ b/src/HOL/Set.ML	Wed Aug 19 10:27:25 1998 +0200
@@ -125,7 +125,7 @@
 (*need UNION, INTER also?*)
 
 (*Image: retain the type of the set being expressed*)
-Blast.overloaded ("op ``", domain_type o domain_type);
+Blast.overloaded ("op ``", domain_type);
 
 (*Rule in Modus Ponens style*)
 Goalw [subset_def] "[| A <= B;  c:A |] ==> c:B";