Solve a 3x3 grid puzzle: all rows must add to 15

gistfile1.clj

(use 'clojure.math.combinatorics)

(def possible-answers (permutations (range 1 10)))

(defn sum-els [coll a b c]
  (+ (nth coll a)
     (nth coll b)
     (nth coll c)))

(defn right-answer [coll]
  (= 15
     (sum-els coll 0 1 2)
     (sum-els coll 3 4 5)
     (sum-els coll 6 7 8)
     (sum-els coll 0 3 6)
     (sum-els coll 1 4 7)
     (sum-els coll 2 5 8)
     (sum-els coll 0 4 8)
     (sum-els coll 2 4 6)))

(def answers (filter right-answer possible-answers))