Sudoku

```clojure
(ns sudoku
  (:refer-clojure :exclude [==])
  (:use clojure.core.logic))

(defn get-square [rows x y]
  (for [x (range x (+ x 3))
        y (range y (+ y 3))]
    (get-in rows [x y])))

(defn init [vars hints]
  (if (seq vars)
    (let [hint (first hints)]
      (all
        (if-not (zero? hint)
          (== (first vars) hint)
          succeed)
        (init (next vars) (next hints))))
    succeed))

(defn sudokufd [hints]
  (let [vars (repeatedly 81 lvar)
        rows (->> vars (partition 9) (map vec) (into []))
        cols (apply map vector rows)
        sqs  (for [x (range 0 9 3)
                   y (range 0 9 3)]
               (get-square rows x y))]
    (run 1 [q]
      (== q vars)
      (everyg #(infd % (domain 1 2 3 4 5 6 7 8 9)) vars)
      (init vars hints)
      (everyg distinctfd rows)
      (everyg distinctfd cols)
      (everyg distinctfd sqs))))

;; ====

(comment
  (sudokufd
    [0 0 3  0 2 0  6 0 0
     9 0 0  3 0 5  0 0 1
     0 0 1  8 0 6  4 0 0

     0 0 8  1 0 2  9 0 0
     7 0 0  0 0 0  0 0 8
     0 0 6  7 0 8  2 0 0

     0 0 2  6 0 9  5 0 0
     8 0 0  2 0 3  0 0 9
     0 0 5  0 1 0  3 0 0])
)