If interested in supporting recursion, the SICP tutorial does a great job supporting it! I chose not to include this for the essay, but it's fun to hack. If you

If interested in supporting recursion, the SICP tutorial does a great job supporting it! I chose not to include this for the essay, but it's fun to hack. If you end up doing this, here's a reference Clojure implementation: https://github.com/nezaj/clj-sicp/blob/master/src/logic_interpreter.clj#L222-L236 https://github.com/nezaj/clj-sicp/blob/master/src/logic_inte... (The main ingredient, if I remember correctly, was `unify-match`)