diff --git a/src/cljam/algo/depth.clj b/src/cljam/algo/depth.clj
index dc79a6b2..3db5159a 100644
--- a/src/cljam/algo/depth.clj
+++ b/src/cljam/algo/depth.clj
@@ -3,7 +3,7 @@
   (:require [com.climate.claypoole :as cp]
             [com.climate.claypoole.lazy :as lazy]
             [cljam.common :as common]
-            [cljam.util :as util]
+            [cljam.util.region :as region]
             [cljam.io.sam :as sam]
             [cljam.io.sam.util :as sam-util])
   (:import [cljam.io.protocols SAMRegionBlock]))
@@ -39,7 +39,7 @@
                                 (fn [[start end]]
                                   (with-open [r (sam/clone-bam-reader rdr)]
                                     (count-for-positions (read-fn r start end) start end))) xs)))]
-    (->> (util/divide-region start end step)
+    (->> (region/divide-region start end step)
          count-fn
          (apply concat))))
 
@@ -108,7 +108,7 @@
       (f (sam/read-blocks rdr region {:mode :region}) start end 0 pile)
       (cp/pdoseq
        n-threads
-       [[s e] (util/divide-region start end step)]
+       [[s e] (region/divide-region start end step)]
        (with-open [r (sam/clone-bam-reader rdr)]
          (-> (sam/read-blocks r {:chr chr, :start s, :end e} {:mode :region})
              (f s e (- s start) pile)))))
diff --git a/src/cljam/tools/cli.clj b/src/cljam/tools/cli.clj
index c2b1c133..4ce1ee7c 100644
--- a/src/cljam/tools/cli.clj
+++ b/src/cljam/tools/cli.clj
@@ -16,7 +16,7 @@
             [cljam.algo.pileup :as plp]
             [cljam.algo.convert :as convert]
             [cljam.algo.level :as level]
-            [cljam.util :as util])
+            [cljam.util.region :as region])
   (:import [java.io Closeable BufferedWriter OutputStreamWriter]))
 
 ;; CLI functions
@@ -267,7 +267,7 @@
         (when-not (sorter/sorted-by? r)
           (exit 1 "Not sorted"))
         (if (:region options)
-          (if-let [region (util/parse-region (:region options))]
+          (if-let [region (region/parse-region (:region options))]
             (cond
               (:simple options) (pileup-simple r (:thread options) region)
               (:ref options) (pileup-with-ref r (:ref options) region)
diff --git a/src/cljam/util.clj b/src/cljam/util.clj
index 04700012..a188e364 100644
--- a/src/cljam/util.clj
+++ b/src/cljam/util.clj
@@ -87,68 +87,3 @@
        (-> (CompressorStreamFactory.)
            (.createCompressorOutputStream s os))
        os))))
-
-;; region utils
-;; ---------
-
-(defn divide-region
-  "Divides a region [start end] into several chunks with maximum length 'step'.
-  Returns a lazy sequence of vector."
-  [start end step]
-  (->> [(inc end)]
-       (concat (range start (inc end) step))
-       (partition 2 1)
-       (map (fn [[s e]] [s (dec e)]))))
-
-(defn divide-refs
-  "Divides refs into several chunks with maximum length 'step'.
-  Returns a lazy sequence of map containing {:chr :start :end}."
-  [refs step]
-  (mapcat
-   (fn [{:keys [name len]}]
-     (map (fn [[s e]] {:chr name :start s :end e})
-          (divide-region 1 len step)))
-   refs))
-
-(defn valid-rname?
-  "Checks if the given rname conforms to the spec of sam."
-  [rname]
-  (and rname (string? rname) (re-matches #"[!-)+-<>-~][!-~]*" rname)))
-
-(defn valid-region?
-  "Checks if the given region map is a valid 1-based closed range."
-  [{:keys [chr start end]}]
-  (and start end
-       (valid-rname? chr)
-       (number? start) (pos? start)
-       (number? end) (pos? end)
-       (<= start end)))
-
-(defn parse-region
-  "Parse a region string into a map."
-  [region-str]
-  (when region-str
-    (let [[_ chr _ start _ end] (re-matches #"([!-)+-<>-~][!-~]*?)(:(\d+)?(-(\d+))?)?" region-str)
-          start' (proton/as-long start)
-          end' (proton/as-long end)]
-      (when chr
-        (cond-> {:chr chr}
-          start' (assoc :start start')
-          end' (assoc :end end'))))))
-
-(defn parse-region-strict
-  "Parse a region string into a map strictly."
-  [region-str]
-  (let [region-map (parse-region region-str)]
-    (when (valid-region? region-map) region-map)))
-
-(defn format-region
-  "Format a region map into a string."
-  [{:keys [chr start end]}]
-  (let [result (apply str (interleave [nil \: \-] (take-while some? [chr start end])))]
-    (when-not (cstr/blank? result) result)))
-
-(defn format-region-strict
-  "Format a region map into a string strictly."
-  [region-map]
-  (when (valid-region? region-map) (format-region region-map)))
diff --git a/src/cljam/util/region.clj b/src/cljam/util/region.clj
new file mode 100644
index 00000000..66c6d230
--- /dev/null
+++ b/src/cljam/util/region.clj
@@ -0,0 +1,157 @@
+(ns cljam.util.region
+  "Utility functions for manipulating chromosomal regions."
+  (:require [clojure.string :as cstr]
+            [proton.core :as proton]))
+
+;;; region conversion
+;;; ----------
+
+(defn merge-regions-with
+  "Returns a lazy sequence of merged regions. Input regions must be sorted.
+  Neighboring regions apart less than or equal to 'max-gap' will be merged
+  with 'merge-fn'. Returns a stateful transducer when no input 'regions' is
+  provided."
+  ([merge-fn]
+   (merge-regions-with merge-fn 0))
+  ([merge-fn ^long max-gap]
+   (fn merge-regions-transducer [rf]
+     (let [last-reg (volatile! nil)]
+       (fn merge-regions-rf
+         ([] (rf))
+         ([r] (rf (if-let [l @last-reg] (rf r l) r)))
+         ([r x] (if-let [l @last-reg]
+                  (if (and (= (:chr l) (:chr x))
+                           (<= (- (dec (:start x)) (:end l)) max-gap))
+                    (do (vswap! last-reg merge-fn x) r)
+                    (do (vreset! last-reg x) (rf r l)))
+                  (do (vreset! last-reg x) r)))))))
+  ([merge-fn ^long max-gap regs]
+   (if-let [f (first regs)]
+     (if-let [s (second regs)]
+       (if (and (= (:chr f) (:chr s))
+                (<= (- (dec (:start s)) (:end f)) max-gap))
+         (let [next-regs (cons (merge-fn f s) (nnext regs))]
+           (lazy-seq (merge-regions-with merge-fn max-gap next-regs)))
+         (cons f (lazy-seq (merge-regions-with merge-fn max-gap (next regs)))))
+       [f])
+     [])))
+
+(defn- merge-two-regions
+  "Default function to merge two regions."
+  [x y]
+  (update x :end max (:end y)))
+
+(def
+  ^{:doc "Same as 'merge-regions-with' except for 'merge-two-regions' is
+  partially applied as merge-fn."
+    :arglists '([] [max-gap] [max-gap regions])}
+  merge-regions
+  (partial merge-regions-with merge-two-regions))
+
+(defn subtract-region
+  "Subtract a region from another one.
+  Returns a vector of regions."
+  [lhs-reg rhs-reg]
+  (if (= (:chr lhs-reg) (:chr rhs-reg))
+    (filterv
+     #(<= (:start %) (:end %))
+     [(update lhs-reg :end min (dec (:start rhs-reg)))
+      (update lhs-reg :start max (inc (:end rhs-reg)))])
+    [lhs-reg]))
+
+(defn complement-regions
+  "Returns a sequence of regions complement to in-regions.
+  in-regions must be sorted.
+  Returns a stateful transducer when no regions provided."
+  ([base-region]
+   (fn [rf]
+     (let [last-reg (volatile! base-region)]
+       (fn
+         ([] (rf))
+         ([r] (rf (if-let [l @last-reg] (rf r l) r)))
+         ([r x]
+          (if-let [l @last-reg]
+            (let [[a b] (subtract-region l x)]
+              (vreset! last-reg (or b a))
+              (if b (rf r a) r))
+            r))))))
+  ([base-region in-regions]
+   (if-let [reg (first in-regions)]
+     (if-let [[a b] (seq (subtract-region base-region reg))]
+       (if b
+         (cons a (lazy-seq (complement-regions b (next in-regions))))
+         (lazy-seq (complement-regions a (next in-regions))))
+       [])
+     [base-region])))
+
+(defn divide-region
+  "Divides a region [start end] into several chunks with maximum length 'step'.
+  Returns a lazy sequence of vector."
+  [start end step]
+  (->> [(inc end)]
+       (concat (range start (inc end) step))
+       (partition 2 1)
+       (map (fn [[s e]] [s (dec e)]))))
+
+(defn divide-refs
+  "Divides refs into several chunks with maximum length 'step'.
+  Returns a lazy sequence of map containing {:chr :start :end}."
+  [refs step]
+  (mapcat
+   (fn [{:keys [name len]}]
+     (map (fn [[s e]] {:chr name :start s :end e})
+          (divide-region 1 len step)))
+   refs))
+
+;;; validation
+;;; ----------
+
+(defn valid-rname?
+  "Checks if the given rname conforms to the spec of sam."
+  [rname]
+  (and rname (string? rname) (re-matches #"[!-)+-<>-~][!-~]*" rname)))
+
+(defn valid-region?
+  "Checks if the given region map is a valid 1-based closed range."
+  [{:keys [chr start end]}]
+  (and start end
+       (valid-rname? chr)
+       (number? start) (pos? start)
+       (number? end) (pos? end)
+       (<= start end)))
+
+;;; region <=> string
+;;; ----------
+
+(defn parse-region
+  "Parse a region string into a map."
+  [region-str]
+  (when region-str
+    (let [pattern #"([!-)+-<>-~][!-~]*?)(:(\d+)?(-(\d+))?)?"
+          [_ chr _ start _ end] (re-matches pattern region-str)
+          start' (proton/as-long start)
+          end' (proton/as-long end)]
+      (when chr
+        (cond-> {:chr chr}
+          start' (assoc :start start')
+          end' (assoc :end end'))))))
+
+(defn parse-region-strict
+  "Parse a region string into a map strictly."
+  [region-str]
+  (let [region-map (parse-region region-str)]
+    (when (valid-region? region-map) region-map)))
+
+(defn format-region
+  "Format a region map into a string."
+  [{:keys [chr start end]}]
+  (let [result (->> [chr start end]
+                    (take-while some?)
+                    (interleave [nil \: \-])
+                    (apply str))]
+    (when-not (cstr/blank? result) result)))
+
+(defn format-region-strict
+  "Format a region map into a string strictly."
+  [region-map]
+  (when (valid-region? region-map) (format-region region-map)))
diff --git a/test/cljam/util/region_test.clj b/test/cljam/util/region_test.clj
new file mode 100644
index 00000000..b6274141
--- /dev/null
+++ b/test/cljam/util/region_test.clj
@@ -0,0 +1,272 @@
+(ns cljam.util.region-test
+  (:require [clojure.test :refer :all]
+            [cljam.util.region :as region]))
+
+(defn into* ([] []) ([r] r) ([r x] (conj r x)))
+
+(deftest merge-regions
+  (testing "(merge-regions)"
+    (are [?regs ?expected]
+        (= (sequence (region/merge-regions) ?regs)
+           (transduce identity ((region/merge-regions) into*) ?regs)
+           ?expected)
+
+      nil
+      []
+
+      []
+      []
+
+      [{:chr "1", :start 1, :end 10}]
+      [{:chr "1", :start 1, :end 10}]
+
+      [{:chr "1", :start 1, :end 10} {:chr "1", :start 1, :end 14}]
+      [{:chr "1", :start 1, :end 14}]
+
+      [{:chr "1", :start 1, :end 10} {:chr "1", :start 10, :end 20}]
+      [{:chr "1", :start 1, :end 20}]
+
+      [{:chr "1", :start 1, :end 10} {:chr "1", :start 11, :end 20}]
+      [{:chr "1", :start 1, :end 20}]
+
+      [{:chr "1", :start 1, :end 10} {:chr "1", :start 12, :end 20}]
+      [{:chr "1", :start 1, :end 10} {:chr "1", :start 12, :end 20}]
+
+      [{:chr "1", :start 1, :end 10} {:chr "1", :start 11, :end 20}
+       {:chr "1", :start 21, :end 30}]
+      [{:chr "1", :start 1, :end 30}]
+
+      [{:chr "1", :start 1, :end 10} {:chr "1", :start 11, :end 20}
+       {:chr "1", :start 22, :end 30}]
+      [{:chr "1", :start 1, :end 20} {:chr "1", :start 22, :end 30}]))
+
+  (testing "(merge-regions gap) and (merge-regions gap regs)"
+    (are [?gap ?regs ?expected]
+        (= (sequence (region/merge-regions ?gap) ?regs)
+           (region/merge-regions ?gap ?regs)
+           ?expected)
+
+      3 nil
+      []
+
+      3 []
+      []
+
+      3 [{:chr "1", :start 1, :end 10}]
+      [{:chr "1", :start 1, :end 10}]
+
+      3 [{:chr "1", :start 1, :end 10} {:chr "1", :start 1, :end 8}]
+      [{:chr "1", :start 1, :end 10}]
+
+      3 [{:chr "1", :start 1, :end 10} {:chr "1", :start 5, :end 14}]
+      [{:chr "1", :start 1, :end 14}]
+
+      3 [{:chr "1", :start 1, :end 10} {:chr "1", :start 13, :end 20}]
+      [{:chr "1", :start 1, :end 20}]
+
+      3 [{:chr "1", :start 1, :end 10} {:chr "1", :start 14, :end 20}]
+      [{:chr "1", :start 1, :end 20}]
+
+      2 [{:chr "1", :start 1, :end 10} {:chr "1", :start 14, :end 20}]
+      [{:chr "1", :start 1, :end 10} {:chr "1", :start 14, :end 20}]
+
+      3 [{:chr "1", :start 1, :end 10} {:chr "1", :start 15, :end 20}]
+      [{:chr "1", :start 1, :end 10} {:chr "1", :start 15, :end 20}]
+
+      3 [{:chr "1", :start 1, :end 10} {:chr "1", :start 14, :end 20}
+         {:chr "1", :start 24, :end 30}]
+      [{:chr "1", :start 1, :end 30}]
+
+      3 [{:chr "1", :start 1, :end 10} {:chr "1", :start 14, :end 20}
+         {:chr "1", :start 25, :end 30}]
+      [{:chr "1", :start 1, :end 20} {:chr "1", :start 25, :end 30}]
+
+      3 [{:chr "1", :start 1, :end 10} {:chr "1", :start 14, :end 20} {:chr "2", :start 24, :end 30}]
+      [{:chr "1", :start 1, :end 20} {:chr "2", :start 24, :end 30}])))
+
+(deftest subtract-region
+  (are [?lhs ?rhs ?expected]
+      (= (region/subtract-region ?lhs ?rhs) ?expected)
+    {:chr "1" :start 10 :end 20} nil
+    [{:chr "1" :start 10 :end 20}]
+
+    {:chr "1" :start 10 :end 20} {:chr "1" :start 1 :end 9}
+    [{:chr "1" :start 10 :end 20}]
+
+    {:chr "1" :start 10 :end 20} {:chr "1" :start 1 :end 10}
+    [{:chr "1" :start 11 :end 20}]
+
+    {:chr "1" :start 10 :end 20} {:chr "1" :start 10 :end 19}
+    [{:chr "1" :start 20 :end 20}]
+
+    {:chr "1" :start 10 :end 20} {:chr "1" :start 11 :end 19}
+    [{:chr "1" :start 10 :end 10} {:chr "1" :start 20 :end 20}]
+
+    {:chr "1" :start 10 :end 20} {:chr "1" :start 10 :end 20}
+    []
+
+    {:chr "1" :start 10 :end 20} {:chr "1" :start 20 :end 30}
+    [{:chr "1" :start 10 :end 19}]
+
+    {:chr "1" :start 10 :end 20} {:chr "1" :start 21 :end 30}
+    [{:chr "1" :start 10 :end 20}]
+
+    {:chr "1" :start 10 :end 20} {:chr "2" :start 10 :end 20}
+    [{:chr "1" :start 10 :end 20}]))
+
+(deftest complement-regions
+  (are [?base-region ?in-region ?expected]
+      (= (sequence (region/complement-regions ?base-region) ?in-region)
+         (transduce identity ((region/complement-regions ?base-region) into*) ?in-region)
+         (region/complement-regions ?base-region ?in-region)
+         ?expected)
+    {:chr "1"  :start 100 :end 200} [] [{:chr "1" :start 100 :end 200}]
+    {:chr "1"  :start 100 :end 200} [{:chr "1" :start 1 :end 99}] [{:chr "1" :start 100 :end 200}]
+    {:chr "1"  :start 100 :end 200} [{:chr "1" :start 201 :end 300}] [{:chr "1" :start 100 :end 200}]
+    {:chr "1"  :start 100 :end 200} [{:chr "1" :start 99 :end 100}] [{:chr "1" :start 101 :end 200}]
+    {:chr "1"  :start 100 :end 200} [{:chr "1" :start 100 :end 150}] [{:chr "1" :start 151 :end 200}]
+    {:chr "1"  :start 100 :end 200} [{:chr "1" :start 100 :end 200}] []
+    {:chr "1"  :start 100 :end 200} [{:chr "1" :start 100 :end 200} {:chr "1" :start 210 :end 230}] []
+    {:chr "1"  :start 100 :end 200} [{:chr "1" :start 150 :end 200}] [{:chr "1" :start 100 :end 149}]
+    {:chr "1"  :start 100 :end 200} [{:chr "1" :start 110 :end 120} {:chr "1" :start 130 :end 140}]
+    [{:chr "1" :start 100 :end 109} {:chr "1" :start 121 :end 129} {:chr "1" :start 141 :end 200}]))
+
+(deftest divide-region
+  (are [?start ?end ?step ?expected]
+      (= (region/divide-region ?start ?end ?step) ?expected)
+    1 10 1 [[1 1] [2 2] [3 3] [4 4] [5 5] [6 6] [7 7] [8 8] [9 9] [10 10]]
+    1 10 2 [[1 2] [3 4] [5 6] [7 8] [9 10]]
+    1 10 3 [[1 3] [4 6] [7 9] [10 10]]
+    1 10 4 [[1 4] [5 8] [9 10]]
+    1 10 5 [[1 5] [6 10]]
+    1 10 6 [[1 6] [7 10]]
+    1 10 7 [[1 7] [8 10]]
+    1 10 8 [[1 8] [9 10]]
+    1 10 9 [[1 9] [10 10]]
+    1 10 10 [[1 10]]
+    1 10 11 [[1 10]]))
+
+(deftest divide-refs
+  (are [?refs ?step ?expected]
+      (= (region/divide-refs ?refs ?step) ?expected)
+    [{:name "chr1" :len 10}] 4 [{:chr "chr1" :start 1 :end 4}
+                                {:chr "chr1" :start 5 :end 8}
+                                {:chr "chr1" :start 9 :end 10}]
+    [{:name "chr1" :len 10}] 5 [{:chr "chr1" :start 1 :end 5}
+                                {:chr "chr1" :start 6 :end 10}]
+    [{:name "chr1" :len 10}] 10 [{:chr "chr1" :start 1 :end 10}]
+    [{:name "chr1" :len 10}
+     {:name "chr2" :len 5}] 6 [{:chr "chr1" :start 1 :end 6}
+                               {:chr "chr1" :start 7 :end 10}
+                               {:chr "chr2" :start 1 :end 5}]))
+
+(deftest valid-rname?
+  (are [?rname ?expected]
+      (= ?expected (boolean (region/valid-rname? ?rname)))
+    nil false
+    [\c \h \r] false
+    "" false
+    "c" true
+    "chr1" true
+    "*" false
+    "=" false
+    ":" true
+    "chr:1" true
+    "chr1:1-10" true))
+
+(deftest valid-region?
+  (are [?region-map ?expected]
+      (= ?expected (boolean (region/valid-region? ?region-map)))
+    nil false
+    {} false
+    {:chr "chr1"} false
+    {:chr "chr1", :start 1} false
+    {:chr "chr1", :start 1, :end 10} true
+    {:chr "chr1", :start 100, :end 10} false
+    {:chr "chr1", :start "1", :end 10} false
+    {:chr "chr1", :start 1, :end "10"} false
+    {:chr "chr1", :start 0, :end 10} false
+    {:chr "chr1", :start 1, :end 0} false
+    {:chr "", :start 100, :end 10} false
+    {:chr " ", :start 100, :end 10} false))
+
+(deftest parse-region
+  (are [?region-str ?expected]
+      (= ?expected (region/parse-region ?region-str))
+    nil nil
+    "*" nil
+    "=" nil
+    "c" {:chr "c"}
+    "chr1" {:chr "chr1"}
+    "chrUn" {:chr "chrUn"}
+    "*chr1" nil
+    "=chr1" nil
+    "chr1*" {:chr "chr1*"}
+    "chr1=" {:chr "chr1="}
+    "chr1-" {:chr "chr1-"}
+    "chr1:" {:chr "chr1"}
+    "chr1:-" {:chr "chr1:-"}
+    "!\"#$%&'()*+,-./0123456789;<=>?@[\\]^_`{|}~" {:chr "!\"#$%&'()*+,-./0123456789;<=>?@[\\]^_`{|}~"}
+    "chr1:1" {:chr "chr1", :start 1}
+    "chr1:1-" {:chr "chr1:1-"}
+    "chr1:1-2" {:chr "chr1", :start 1, :end 2}
+    "chr1:-2" {:chr "chr1", :end 2}
+    "chr1:001-200" {:chr "chr1", :start 1, :end 200}
+    "chr1:100-2" {:chr "chr1", :start 100, :end 2}
+    "chr1:2:3-4" {:chr "chr1:2", :start 3, :end 4}
+    "chr1:2-3:4-5" {:chr "chr1:2-3", :start 4, :end 5}
+    "chr1:2-3:4-5:6-7" {:chr "chr1:2-3:4-5", :start 6, :end 7}))
+
+(deftest parse-region-strict
+  (are [?region-str ?expected]
+      (= ?expected (region/parse-region-strict ?region-str))
+    nil nil
+    "*" nil
+    "=" nil
+    "c" nil
+    "chr1" nil
+    "chrUn" nil
+    "*chr1" nil
+    "=chr1" nil
+    "chr1*" nil
+    "chr1=" nil
+    "chr1-" nil
+    "chr1:" nil
+    "chr1:-" nil
+    "!\"#$%&'()*+,-./0123456789;<=>?@[\\]^_`{|}~" nil
+    "chr1:1" nil
+    "chr1:1-" nil
+    "chr1:1-2" {:chr "chr1", :start 1, :end 2}
+    "chr1:-2" nil
+    "chr1:001-200" {:chr "chr1", :start 1, :end 200}
+    "chr1:100-2" nil
+    "chr1:2:3-4" {:chr "chr1:2", :start 3, :end 4}
+    "chr1:2-3:4-5" {:chr "chr1:2-3", :start 4, :end 5}
+    "chr1:2-3:4-5:6-7" {:chr "chr1:2-3:4-5", :start 6, :end 7}))
+
+(deftest format-region
+  (are [?region-map ?expected]
+      (= ?expected (region/format-region ?region-map))
+    nil nil
+    {} nil
+    {:chr "chr1"} "chr1"
+    {:chr "chr1", :start 1} "chr1:1"
+    {:chr "chr1", :start 1, :end 10} "chr1:1-10"
+    {:chr "chr1", :start 10, :end 1} "chr1:10-1"
+    {:chr "chr1", :end 10} "chr1"
+    {:start 1} nil
+    {:end 10} nil))
+
+(deftest format-region-strict
+  (are [?region-map ?expected]
+      (= ?expected (region/format-region-strict ?region-map))
+    nil nil
+    {} nil
+    {:chr "chr1"} nil
+    {:chr "chr1", :start 1} nil
+    {:chr "chr1", :start 1, :end 10} "chr1:1-10"
+    {:chr "chr1", :start 10, :end 1} nil
+    {:chr "chr1", :end 10} nil
+    {:start 1} nil
+    {:end 10} nil))
+
diff --git a/test/cljam/util_test.clj b/test/cljam/util_test.clj
index 47db5449..f316aa27 100644
--- a/test/cljam/util_test.clj
+++ b/test/cljam/util_test.clj
@@ -12,141 +12,3 @@
   (are [?n] (thrown? AssertionError (util/ubyte ?n))
     -1
     256))
-
-(deftest divide-region
-  (are [?start ?end ?step ?expected]
-      (= (util/divide-region ?start ?end ?step) ?expected)
-    1 10 1 [[1 1] [2 2] [3 3] [4 4] [5 5] [6 6] [7 7] [8 8] [9 9] [10 10]]
-    1 10 2 [[1 2] [3 4] [5 6] [7 8] [9 10]]
-    1 10 3 [[1 3] [4 6] [7 9] [10 10]]
-    1 10 4 [[1 4] [5 8] [9 10]]
-    1 10 5 [[1 5] [6 10]]
-    1 10 6 [[1 6] [7 10]]
-    1 10 7 [[1 7] [8 10]]
-    1 10 8 [[1 8] [9 10]]
-    1 10 9 [[1 9] [10 10]]
-    1 10 10 [[1 10]]
-    1 10 11 [[1 10]]))
-
-(deftest divide-refs
-  (are [?refs ?step ?expected]
-      (= (util/divide-refs ?refs ?step) ?expected)
-    [{:name "chr1" :len 10}] 4 [{:chr "chr1" :start 1 :end 4}
-                                {:chr "chr1" :start 5 :end 8}
-                                {:chr "chr1" :start 9 :end 10}]
-    [{:name "chr1" :len 10}] 5 [{:chr "chr1" :start 1 :end 5}
-                                {:chr "chr1" :start 6 :end 10}]
-    [{:name "chr1" :len 10}] 10 [{:chr "chr1" :start 1 :end 10}]
-    [{:name "chr1" :len 10}
-     {:name "chr2" :len 5}] 6 [{:chr "chr1" :start 1 :end 6}
-                               {:chr "chr1" :start 7 :end 10}
-                               {:chr "chr2" :start 1 :end 5}]))
-
-(deftest valid-rname?
-  (are [?rname ?expected]
-      (= ?expected (boolean (util/valid-rname? ?rname)))
-    nil false
-    "" false
-    "c" true
-    "chr1" true
-    "*" false
-    "=" false
-    ":" true
-    "chr:1" true
-    "chr1:1-10" true))
-
-(deftest valid-region?
-  (are [?region-map ?expected]
-      (= ?expected (boolean (util/valid-region? ?region-map)))
-    nil false
-    {} false
-    {:chr "chr1"} false
-    {:chr "chr1", :start 1} false
-    {:chr "chr1", :start 1, :end 10} true
-    {:chr "chr1", :start 100, :end 10} false
-    {:chr "chr1", :start "1", :end 10} false
-    {:chr "chr1", :start 1, :end "10"} false
-    {:chr "chr1", :start 0, :end 10} false
-    {:chr "chr1", :start 1, :end 0} false
-    {:chr "", :start 100, :end 10} false
-    {:chr " ", :start 100, :end 10} false))
-
-(deftest parse-region
-  (are [?region-str ?expected]
-      (= ?expected (util/parse-region ?region-str))
-    nil nil
-    "*" nil
-    "=" nil
-    "c" {:chr "c"}
-    "chr1" {:chr "chr1"}
-    "chrUn" {:chr "chrUn"}
-    "*chr1" nil
-    "=chr1" nil
-    "chr1*" {:chr "chr1*"}
-    "chr1=" {:chr "chr1="}
-    "chr1-" {:chr "chr1-"}
-    "chr1:" {:chr "chr1"}
-    "chr1:-" {:chr "chr1:-"}
-    "!\"#$%&'()*+,-./0123456789;<=>?@[\\]^_`{|}~" {:chr "!\"#$%&'()*+,-./0123456789;<=>?@[\\]^_`{|}~"}
-    "chr1:1" {:chr "chr1", :start 1}
-    "chr1:1-" {:chr "chr1:1-"}
-    "chr1:1-2" {:chr "chr1", :start 1, :end 2}
-    "chr1:-2" {:chr "chr1", :end 2}
-    "chr1:001-200" {:chr "chr1", :start 1, :end 200}
-    "chr1:100-2" {:chr "chr1", :start 100, :end 2}
-    "chr1:2:3-4" {:chr "chr1:2", :start 3, :end 4}
-    "chr1:2-3:4-5" {:chr "chr1:2-3", :start 4, :end 5}
-    "chr1:2-3:4-5:6-7" {:chr "chr1:2-3:4-5", :start 6, :end 7}))
-
-(deftest parse-region-strict
-  (are [?region-str ?expected]
-      (= ?expected (util/parse-region-strict ?region-str))
-    nil nil
-    "*" nil
-    "=" nil
-    "c" nil
-    "chr1" nil
-    "chrUn" nil
-    "*chr1" nil
-    "=chr1" nil
-    "chr1*" nil
-    "chr1=" nil
-    "chr1-" nil
-    "chr1:" nil
-    "chr1:-" nil
-    "!\"#$%&'()*+,-./0123456789;<=>?@[\\]^_`{|}~" nil
-    "chr1:1" nil
-    "chr1:1-" nil
-    "chr1:1-2" {:chr "chr1", :start 1, :end 2}
-    "chr1:-2" nil
-    "chr1:001-200" {:chr "chr1", :start 1, :end 200}
-    "chr1:100-2" nil
-    "chr1:2:3-4" {:chr "chr1:2", :start 3, :end 4}
-    "chr1:2-3:4-5" {:chr "chr1:2-3", :start 4, :end 5}
-    "chr1:2-3:4-5:6-7" {:chr "chr1:2-3:4-5", :start 6, :end 7}))
-
-(deftest format-region
-  (are [?region-map ?expected]
-      (= ?expected (util/format-region ?region-map))
-    nil nil
-    {} nil
-    {:chr "chr1"} "chr1"
-    {:chr "chr1", :start 1} "chr1:1"
-    {:chr "chr1", :start 1, :end 10} "chr1:1-10"
-    {:chr "chr1", :start 10, :end 1} "chr1:10-1"
-    {:chr "chr1", :end 10} "chr1"
-    {:start 1} nil
-    {:end 10} nil))
-
-(deftest format-region-strict
-  (are [?region-map ?expected]
-      (= ?expected (util/format-region-strict ?region-map))
-    nil nil
-    {} nil
-    {:chr "chr1"} nil
-    {:chr "chr1", :start 1} nil
-    {:chr "chr1", :start 1, :end 10} "chr1:1-10"
-    {:chr "chr1", :start 10, :end 1} nil
-    {:chr "chr1", :end 10} nil
-    {:start 1} nil
-    {:end 10} nil))