[plt-scheme] Names in signatures

Is it possible to do something like the following:

  (define-signature list^
    (empty cons car cdr))

  (define-signature catenable-list^
    ((open list^)
     append))

  (define-signature double-ended-list^
    ((open list^)
      snoc))

  (define-signature catenable-double-ended-list^
    ((open double-ended-list)
     (open catenable-list)))

The last signature is giving me problems. The syntax checker
says that some names are defined multple times, and that's
true. But in this case it on purpose.

NB: I am sitting on a computer without Scheme, so the
above is not syntax-checked.

-- 
Jens Axel Søgaard