gistfile1.clj

(defn solve
  "Solve a system of equations by constraint propagation"
  [equations known]
  (dbg :student (format "SOLVE %s %s" equations known))
  (or
   (some (fn [equation]
           (let [x (one-unknown equation)]
             (when x
               (let [answer (solve-arithmetic (isolate equation x))]
                 (solve (postwalk-replace {(:lhs answer) (:rhs answer)}
                                          (remove (partial = equation) equations))
                        (cons answer known))))))
         equations)
   known))