book module->edit own book pages does not allow book page deletion

(basic book module question drupal-4.7.4)
how do I allow a "authenticated user" to delete his own page?
the "delete" button when the book page is edited is only there if the "user" has (node module->administer nodes checked) :(
but when the "user" has "administer node" he can delete any node, not only his own. :(

edit own {blog,story} has the expected behaviour: one can delete his own page.

[tru@drupal modules]$ rcsdiff -u book.module
===================================================================
RCS file: book.module,v
retrieving revision 1.1
diff -u -r1.1 book.module
--- book.module 2006/11/09 19:09:41     1.1
+++ book.module 2006/11/09 19:10:26
@@ -32,7 +32,7 @@
     return user_access('create book pages');
   }
 
-  if ($op == 'update') {
+  if ($op == 'update' || $op == 'delete') {
     // Only registered users can update book pages.  Given the nature
     // of the book module this is considered to be a good/safe idea.
     // One can only update a book page if there are no suggested updates

gives the expected behviour, but the "delete" action never returns (it's my 1st php code modification).

Can someone help?

Thanks

Tru
ref:
http://drupal.org/node/21559
http://drupal.org/node/78905