Solution of Polish Scrabble riddle at http://trzeciblank.wordpress.com/2014/07/31/zagadka-piecioliterowce/

gistfile1.clj

(ns trzeciblank
  (:require [clojure.string :as string]
            [clojure.java.io :as io]
            [clojure.set :refer :all]))

(def piatki (set (line-seq (io/reader "/home/nathell/scrabble/w5.txt"))))

(defn kandydaci [slowo]
  (for [i (range 5) x "abcdefghijklmnoprstuwyząćęłńóśźż"
        :let [kand (str (subs slowo 0 i) x (subs slowo (inc i)))]
        :when (piatki kand)]
    kand))

(defn szukaj 
  ([slowo] (szukaj #{slowo} #{}))
  ([slowa widziane]
     (if (empty? slowa)
       widziane
       (let [slowo (first slowa)
             reszta (disj slowa slowo)
             widziane (conj widziane slowo) 
             nowe (difference (set (kandydaci slowo)) widziane)]
         (recur (union nowe reszta) widziane)))))

(print (string/join " " (map string/upper-case (sort (difference piatki (szukaj "blank"))))))