Hi Charles,
thanks a lot for posting this, since I also recognized some time ago it did not work any more and had no time to try out how it works now.
For interested users, I attach an old paper from Herbert Diehl describing in more detail how the method worked in Mechanica 8.0 (! :-)). I also add two simple models that may help users to understand what an "anti-symmetric" constraint is. It's a bit tricky!
Best,
Roland