Very nice! Thanks.
You might be interested in this paper and code on the implementation of microKanren, a minimal implementation of core miniKanren. The core implementation is under 50 lines of Scheme code.
Jason Hemann and Daniel P. Friedman. microKanren: A Minimal Functional Core for Relational Programming. In Proceedings of the 2013 Workshop on Scheme and Functional Programming (Scheme '13), Alexandria, VA, 2013.