[plt-scheme] except-out?

You would do me a great favor by telling what is wrong in:

(module a scheme (provide (except-out scheme +)))

Welcome to DrScheme, version 3.99.0.10-svn31jan2008 [3m].
Language: Module.
except-out: identifier `+' not included in nested provide spec in: scheme

Kind regards, Jos Koot
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.racket-lang.org/users/archive/attachments/20080201/ceaff5fb/attachment.html>