gistfile1.txt

(define (unify a b)
  (cond ((and (pair? a)
              (pair? b)) (cons (unify (car a) (car b))
                               (unify (cdr a) (cdr b))))

        ((symbol? a) b) ; here i just return b, because a symbol matches anything. a more complex system would have a third argument
                        ; , the environment, that tracks existing bindings for a, and prevents conflicts. then, instead of returning b
                        ; we could update the environment with the binding for a = b, or issue a failure (in kanren language, #u)

        ((eq? a b) b)   ; a and b trivially unify without updating any bindings. here I just return their mutual value

        (else (error)))) ; nope, that's a #u