src/HOL/Update.ML

+(*  Title:      HOL/UNITY/Update.thy
+    ID:         $Id$
+    Author:     Lawrence C Paulson, Cambridge University Computer Laboratory
+    Copyright   1998  University of Cambridge
+
+Function updates: like the standard theory Map, but for ordinary functions
+*)
+
+open Update;
+
+goalw thy [update_def] "(f[x:=y] = f) = (f x = y)";
+by Safe_tac;
+by (etac subst 1);
+by (rtac ext 2);
+by Auto_tac;
+qed "update_idem_iff";
+
+(* f x = y ==> f[x:=y] = f *)
+bind_thm("update_idem", update_idem_iff RS iffD2);
+
+AddIffs [refl RS update_idem];
+
+goal thy "(f[x:=y])z = (if x=z then y else f z)";
+by (simp_tac (simpset() addsimps [update_def]) 1);
+qed "update_apply";
+Addsimps [update_apply];