sample.clj

(ns foo.coloring-tn
  (:require [clojure.core.logic :refer :all]
            [clojure.core.logic.pldb :as pldb]))


(def facts
  (pldb/db
   [color 'red]
   [color 'green]
   [color 'blue]
   [color 'pink]
   ))

(defn neighbor [state-a state-b]
  (all
   (color state-a)
   (color state-b)
   (!= state-a state-b)))


(let [states '[A B C]
      res (pldb/with-db facts (run 1 [q]
                                      (fresh [A B C]
                                        (neighbor A B)
                                        (neighbor B C)
                                        (== q [A B C]))))]
        (map #(zipmap states %) res))