[racket] Redex multi-hole contexts

So in attempting to model an abstract machine for a parallel language (pH), I found it very unpleasant to use Redex.  I didn't care about the non-determinism resulting from which thread might possibly be executing at the moment; they should all conceptually be running in parallel, with the order being unimportant.

Matthias mentioned that at one point Redex had multi-hole contexts, but that they were taken out and he doesn't remember why.  Does anyone know?

Thanks,

Alex