Original Christophe Grand's solution

src/dojo/life.clj

@@ -4,14 +4,13 @@
 
 (ns dojo.life)
 
-; http://rosettacode.org/wiki/Conway's_Game_of_Life#Clojure
+; http://clj-me.cgrand.net/2011/08/19/conways-game-of-life/
 
 (defn neighbours [[x y]]
-  (for [dx [-1 0 1] dy [-1 0 1]
-        :when (not (and (zero? dx) (zero? dy)))]
+  (for [dx [-1 0 1] dy (if (zero? dx) [-1 1] [-1 0 1])]
     [(+ x dx) (+ y dy)]))
 
 (defn next-step [cells]
-  (set (for [[cell n] (frequencies (mapcat neighbours cells))
-             :when (or (= n 3) (and (= n 2) (some #{cell} cells)))]
-         cell)))
+  (set (for [[loc n] (frequencies (mapcat neighbours cells))
+             :when (or (= n 3) (and (= n 2) (cells loc)))]
+         loc)))