error loading (system foreign) in r6rs mode

[Marco Maggi]

On a i686-pc-linux-gnu running Guile 2.0.7 doing:

   $ guile -x .sls -L . proof.sps

with the program:

   #!r6rs
   (import (rnrs) (proof))

and the library:

   #!r6rs
   (library (proof)
     (export libz)
     (import (rnrs)
       (system foreign))
     (define libz
       (dynamic-link "libz.so")))

I get the error:

;;; WARNING: compilation of /home/marco/var/tmp/proof.sps failed:
;;; ERROR: In procedure module-lookup: Unbound variable: dynamic-link

  But the program:

   #!r6rs
   (import (rnrs)
     (system foreign))
   (define libz
     (dynamic-link "libz.so"))
   (display libz)
   (newline)

succeeds with no problems.  Is (system foreign) special?
-- 
Marco Maggi