Definition of unique relation no longer works with racket 6.9

[Moritz Kiefer]

First of all let me thank you for this awesome tutorial!
When I try to define the unique relation as shown in the tutorial

(define-relation REDEX
  unique ⊆ any × ...
  [(unique any_!_1 ...)])

racket complains with define-relation: found an ellipsis outside of a sequence. I tried wrapping it in parenthesis hoping to fix the error and indeed the definition is then accepted. However, when I try to use it via
(judgment-holds (unique 1 2)) I get

unique: relation values do not match the contract;
  contract: (unique (any × ...))
  values: (unique 1 2)

Any ideas how to update this for the new version? I took a look at the docs but I couldn’t find anything helpful (I’m new to both racket and redex).

[Moritz Kiefer]

I found a workaround by using a relation over a list instead of an n-ary relation, i.e.,

(define-judgment-form REDEX
    #:mode (unique I)
    #:contract (unique (any ...))
    [------------------
     (unique (any_!_1 ...))])

I’m still not sure how to define n-ary relations or if this is simply no longer possible.

[David Van Horn]

Thanks!!