diff --git a/src/challenge/core.clj b/src/challenge/core.clj
index b55f937..b0df51f 100644
--- a/src/challenge/core.clj
+++ b/src/challenge/core.clj
@@ -24,13 +24,13 @@
   (union [this other]
     (when-not (.isConnected this other)
       (throw (ex-info "Cannot union non-connecting ranges" {})))
-    (.union this other))
-  (before [^LocalDateRange this ^LocalDate x]
-    (.isBefore this x))
-  (after [this ^LocalDate x]
-    (.isAfter (.getEndInclusive this) x)))
+    (.union this other)))
+
+(def ^:private closed-local-date-range
+  (memoize (fn [start end]
+             (LocalDateRange/ofClosed start end))))
 
 (defmethod range/->discrete-value-range :local-date-range [_ start end]
-  (LocalDateRange/ofClosed start end))
+  (closed-local-date-range start end))
 
 (def difference range/difference)
diff --git a/src/challenge/discrete_value_range.clj b/src/challenge/discrete_value_range.clj
index fb9ff08..726e573 100644
--- a/src/challenge/discrete_value_range.clj
+++ b/src/challenge/discrete_value_range.clj
@@ -26,7 +26,7 @@
       that before/after values against other values that the range
       is over.
   "
-  (abuts [this ^DiscreteValueRange other])
+  (abuts [this other])
   (value-before [this])
   (value-after [this])
   (start [this])
@@ -34,6 +34,18 @@
   (range-type [this])
   (union [this other]))
 
+(defn ->range-boundaries* [range]
+  [{:value (start range)
+    :boundary-type :start
+    :type (range-type range)
+    :prev-value (value-before range)}
+   {:value (end range)
+    :boundary-type :end
+    :type (range-type range)
+    :next-value (value-after range)}])
+
+(def ->range-boundaries (memoize ->range-boundaries*))
+
 (defn- ordered-range-values
   "Builds an ordered list or 'fenceposts' for the start and end
   of all given ranges, to prepare to produces a consolidated
@@ -48,15 +60,7 @@
   any intermediate matching starts/stops."
   [ranges]
   (->> ranges
-       (mapcat (fn [range]
-                 [{:value (start range)
-                   :boundary-type :start
-                   :type (range-type range)
-                   :prev-value (value-before range)}
-                  {:value (end range)
-                   :boundary-type :end
-                   :type (range-type range)
-                   :next-value (value-after range)}]))
+       (mapcat ->range-boundaries)
        (sort-by (juxt :value (comp {:start 0 :end 1} :boundary-type)))))
 
 (defmulti ->discrete-value-range (fn [range-type _start _end]
@@ -77,25 +81,25 @@
   end pairs encountered between the new start and end values."
   []
   (fn [xf]
-    (let [stack (volatile! [])
+    (let [stack (java.util.Stack.)
           start (volatile! nil)]
       (fn
         ([] (xf))
         ([result] (xf result))
-        ([result input]
+        ([result {:keys [boundary-type value type] :as input}]
          (if (reduced? input)
            result
-           (case (:boundary-type input)
-             :start  (do
-                       (when-not (seq @stack)
-                         (vreset! start (:value input)))
-                       (vswap! stack (fnil conj []) input)
-                       result)
+           (case boundary-type
+             :start (do
+                      (when (.empty stack)
+                        (vreset! start value))
+                      (.push stack input)
+                      result)
              :end (do
-                    (vswap! stack pop)
-                    (if (seq @stack)
+                    (.pop stack)
+                    (if (not (.empty stack))
                       result
-                      (xf result (->discrete-value-range (:type input) @start (:value input))))))))))))
+                      (xf result (->discrete-value-range type @start value)))))))))))
 
 (defn- combine-abutting-ranges
   "transducer to join ranges where the start and end of two ranges are consective
@@ -124,9 +128,9 @@
              (vreset! prev item)
              result)
 
-           :else  (let [item @prev]
-                    (vreset! prev input)
-                    (xf result item))))))))
+           :else (let [item @prev]
+                   (vreset! prev input)
+                   (xf result item))))))))
 
 (def consolidate-ranges-xf
   (comp
@@ -138,18 +142,17 @@
 
 (defn walk-range-boundaries [range-boundary-items]
   (let [close-working-range (fn [range-type start end ranges]
-                              (conj ranges (->discrete-value-range range-type
-                                                                   start
-                                                                   end)))]
-
+                              (conj! ranges (->discrete-value-range range-type
+                                                                    start
+                                                                    end)))]
     (loop [[boundary-item & boundary-items] range-boundary-items
            in-filter-range nil
            in-source-range nil
-           ranges #{}
+           ranges (transient #{})
            close-fn nil]
       (match [boundary-item]
         [nil]
-        ranges
+        (persistent! ranges)
 
         [{:boundary-type :start
           :range-source-type :source-range
diff --git a/test/challenge/discrete_value_range_test.clj b/test/challenge/discrete_value_range_test.clj
index ca7c86d..92fcaa5 100644
--- a/test/challenge/discrete_value_range_test.clj
+++ b/test/challenge/discrete_value_range_test.clj
@@ -31,10 +31,12 @@
   (toString [_this]
     (str start ".." end)))
 
-(defn int-range-inclusive [start end]
+(defn- int-range-inclusive* [start end]
   (assert (<= start end) (str "start : " start "; end: " end))
   (->IntInclusiveDiscreteValueRange start end))
 
+(def int-range-inclusive (memoize int-range-inclusive*))
+
 (defmethod range/->discrete-value-range :int-range-inclusive [_ start end]
   (int-range-inclusive start end))