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new theorem inv_f_eq
authorpaulson
Wed, 25 Aug 1999 10:45:41 +0200
changeset 7338 b275ae194e5a
parent 7337 3f8eeb0b6d75
child 7339 1b4d7a851b34
new theorem inv_f_eq
src/HOL/Fun.ML file | annotate | diff | comparison | revisions 
--- a/src/HOL/Fun.ML	Tue Aug 24 23:28:02 1999 +0200
+++ b/src/HOL/Fun.ML	Wed Aug 25 10:45:41 1999 +0200
@@ -117,8 +117,12 @@
 Goalw [inv_def] "inj(f) ==> inv f (f x) = x";
 by (etac inj_select 1);
 qed "inv_f_f";
+Addsimps [inv_f_f];
 
-Addsimps [inv_f_f];
+Goal "[| inj(f);  f x = y |] ==> inv f y = x";
+by (etac subst 1);
+by (etac inv_f_f 1);
+qed "inv_f_eq";
 
 (* Useful??? *)
 val [oneone,minor] = Goal
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