diff --git a/ch03-game-of-life/src/com/clojurebook/collections/life.clj b/ch03-game-of-life/src/com/clojurebook/collections/life.clj
index fe8babc..62f2be6 100644
--- a/ch03-game-of-life/src/com/clojurebook/collections/life.clj
+++ b/ch03-game-of-life/src/com/clojurebook/collections/life.clj
@@ -1,148 +1,12 @@
 (ns com.clojurebook.collections.life)
 
-(defn empty-board
-  "Creates a rectangular empty board of the specified width
-   and height."
-  [w h]
-  (vec (repeat w (vec (repeat h nil)))))
+(defn neighbours [[x y]]
+  (for [dx [-1 0 1] dy [-1 0 1] :when (not= 0 dx dy)]
+    [(+ x dx) (+ y dy)]))
 
-
-(defn populate
-  "Turns :on each of the cells specified as [y, x] coordinates."
-  [board living-cells]
-  (reduce (fn [board coordinates]
-            (assoc-in board coordinates :on))
-          board
-          living-cells))
-
-(def glider (populate (empty-board 6 6) #{[2 0] [2 1] [2 2] [1 2] [0 1]}))
-
-(defn neighbours
-  [[x y]]
-  (for [dx [-1 0 1] dy [-1 0 1] :when (not= 0 dx dy)] 
-    [(+ dx x) (+ dy y)]))
-
-(defn count-neighbours
-  [board loc]
-  (count (filter #(get-in board %) (neighbours loc))))
-
-(defn indexed-step 
-  "Yields the next state of the board, using indices to determine neighbors,
-   liveness, etc."
-  [board]
-  (let [w (count board)
-        h (count (first board))]
-    (loop [new-board board x 0 y 0]
-      (cond
-        (>= x w) new-board
-        (>= y h) (recur new-board (inc x) 0)
-        :else
-          (let [new-liveness
-                 (case (count-neighbours board [x y])
-                   2 (get-in board [x y])
-                   3 :on
-                   nil)]
-            (recur (assoc-in new-board [x y] new-liveness) x (inc y)))))))
-
-
-(defn indexed-step2
-  [board]
-  (let [w (count board)
-        h (count (first board))]
-    (reduce 
-      (fn [new-board x]
-        (reduce 
-          (fn [new-board y]
-            (let [new-liveness
-                   (case (count-neighbours board [x y])
-                     2 (get-in board [x y])
-                     3 :on
-                     nil)]
-              (assoc-in new-board [x y] new-liveness)))
-          new-board (range h)))
-      board (range w))))
-
-
-(defn indexed-step3
-  [board]
-  (let [w (count board)
-        h (count (first board))]
-    (reduce 
-      (fn [new-board [x y]]
-        (let [new-liveness
-               (case (count-neighbours board [x y])
-                 2 (get-in board [x y])
-                 3 :on
-                 nil)]
-           (assoc-in new-board [x y] new-liveness)))
-      board (for [x (range h) y (range w)] [x y]))))
-
-
-(defn window
-  "Returns a lazy sequence of 3-item windows centered
-   around each item of coll, padded as necessary with
-   pad or nil."
-  ([coll] (window nil coll))
-  ([pad coll]
-   (partition 3 1 (concat [pad] coll [pad]))))
-
-(defn cell-block 
-  "Creates a sequences of 3x3 windows from a triple of 3 sequences."
-  [[left mid right]]
-  (window (map vector left mid right))) 
-
-(defn liveness
-  "Returns the liveness (nil or :on) of the center cell for
-   the next step."  
-  [block]
-  (let [[_ [_ center _] _] block]
-    (case (- (count (filter #{:on} (apply concat block)))
-             (if (= :on center) 1 0))
-      2 center
-      3 :on
-      nil)))
-
-(defn- step-row
-  "Yields the next state of the center row."
-  [rows-triple]
-  (vec (map liveness (cell-block rows-triple)))) 
-
-(defn index-free-step
-  "Yields the next state of the board."
-  [board]
-  (vec (map step-row (window (repeat nil) board))))
-
-(defn step 
- "Yields the next state of the world"
- [cells]
- (set (for [[loc n] (frequencies (mapcat neighbours cells))
-            :when (or (= n 3) (and (= n 2) (cells loc)))]
-        loc)))
-
-(defn stepper 
-  "Returns a step function for Life-like cell automata.
-   neighbours takes a location and return a sequential collection
-   of locations. survive? and birth? are predicates on the number
-   of living neighbours."
-  [neighbours birth? survive?] 
-  (fn [cells]
-    (set (for [[loc n] (frequencies (mapcat neighbours cells))
-               :when (if (cells loc) (survive? n) (birth? n))]
-           loc))))
-
-(defn hex-neighbours
-  [[x y]]
-  (for [dx [-1 0 1] dy (if (zero? dx) [-2 2] [-1 1])] 
-    [(+ dx x) (+ dy y)]))
-
-(def hex-step (stepper hex-neighbours #{2} #{3 4}))
-
-(defn rect-stepper 
-  "Returns a step function for standard game of life on a (bounded) rectangular
-   board of specified size."
-  [w h]
-  (stepper #(filter (fn [[i j]] (and (< -1 i w) (< -1 j h))) 
-                    (neighbours %)) #{2 3} #{3}))
+(defn step [cells]
+  (set (map first (filter #(or (= 3 (second %)) (and (= 2 (second %)) (cells (first %))))
+                          (frequencies (apply concat (map neighbours cells)))))))
 
 (defn draw
   [w h step cells]
@@ -171,5 +35,5 @@
               (.repaint pane)))))
 
 (defn rect-demo []
-  (draw 30 30 (rect-stepper 30 30) 
-      #{[15 15] [15 17] [16 16] [15 16]}))
\ No newline at end of file
+  (draw 30 30 step
+      #{[15 15] [15 17] [16 16] [15 16]}))