Many thanks for the info. I'll have to delve into cKanren more - I kind of glossed over it.

For anyone else interested, it looks like Claire Alvis is leading development of cKanren. Here's a background paper and a link to the source on github:

http://scheme2011.ucombinator.org/papers/Alvis2011.pdf

https://github.com/calvis/cKanren

And here's a short example and discussion of use of cKanren by (I think) one of the core.logic creators:

http://dosync.posterous.com/another-taste-of-ckanren

http://groups.google.com/group/clojure/browse_thread/thread/...

Also, the Friedman group maintains some other source here:

https://github.com/iucs/relational-research

which includes...wait for it...babyMiniKanren (babymk)!