diff --git a/ChangeLog.md b/ChangeLog.md
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -14,4 +14,9 @@
   Removed the low-level functions findSeq and existsSeq
   from the API because they do not suggest the assumptions made.
 
+- 0.2.0.1 updated the documentation of NonNestedSeq and 
+  improved the test case generation of sequences of non-nested intervals. 
+  Replaced Data.List.isSubsequencOf by a custom relation that 
+  reflects our intention to check for contiguous subsequences.  
+
 ## Unreleased changes
diff --git a/closed-intervals.cabal b/closed-intervals.cabal
--- a/closed-intervals.cabal
+++ b/closed-intervals.cabal
@@ -1,7 +1,7 @@
 cabal-version: 1.12
 
 name:           closed-intervals
-version:        0.2.0.0
+version:        0.2.0.1
 synopsis:       Closed intervals of totally ordered types
 description:    see README.md
 author:         Olaf Klinke, Henning Thielemann
@@ -53,7 +53,6 @@
   other-modules:
     Test.Data.Interval
 
--- internal use only
--- source-repository head
---  type:     svn
---  location: svn://192.168.4.220/closed-intervals
+source-repository head
+  type:     darcs
+  location: https://hub.darcs.net/olf/closed-intervals
diff --git a/doctest/Test/Data/Interval.hs b/doctest/Test/Data/Interval.hs
--- a/doctest/Test/Data/Interval.hs
+++ b/doctest/Test/Data/Interval.hs
@@ -16,309 +16,310 @@
 import     Data.Foldable (toList)
 import     Test.QuickCheck ((==>))
 without'     :: (Int,Int) -> (Int,Int) -> [(Int,Int)]; without' = without
+isSubsequenceOf     :: Eq a => [a] -> [a] -> Bool; isSubsequenceOf [] _ = True; isSubsequenceOf (_:_) [] = False; isSubsequenceOf xs@(x:xs') (y:ys) = (x == y && xs' `List.isPrefixOf` ys) || xs `isSubsequenceOf` ys
 
 test :: DocTest.T ()
 test = do
- DocTest.printPrefix "Data.Interval:181: "
-{-# LINE 181 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:189: "
+{-# LINE 189 "src/Data/Interval.hs" #-}
  DocTest.property
-{-# LINE 181 "src/Data/Interval.hs" #-}
+{-# LINE 189 "src/Data/Interval.hs" #-}
         (forevery genNonNestedIntervalSeq $ \xs -> propSplit (\subseq -> hullSeqNonNested subseq == hullSeq subseq) (splitSeq xs))
- DocTest.printPrefix "Data.Interval:176: "
-{-# LINE 176 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:177: "
+{-# LINE 177 "src/Data/Interval.hs" #-}
  DocTest.example
-{-# LINE 176 "src/Data/Interval.hs" #-}
+{-# LINE 177 "src/Data/Interval.hs" #-}
       (propSplit (\xs -> hullSeqNonNested xs == hullSeq xs) . splitSeq . sortByRight $ Seq.fromList ([(1,3),(2,4),(4,5),(3,6)] :: [(Int,Int)]))
   [ExpectedLine [LineChunk "False"]]
- DocTest.printPrefix "Data.Interval:229: "
-{-# LINE 229 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:237: "
+{-# LINE 237 "src/Data/Interval.hs" #-}
  DocTest.property
-{-# LINE 229 "src/Data/Interval.hs" #-}
+{-# LINE 237 "src/Data/Interval.hs" #-}
         (forevery genInterval     $ \i -> overlapTime i i == intervalDuration i)
- DocTest.printPrefix "Data.Interval:230: "
-{-# LINE 230 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:238: "
+{-# LINE 238 "src/Data/Interval.hs" #-}
  DocTest.property
-{-# LINE 230 "src/Data/Interval.hs" #-}
+{-# LINE 238 "src/Data/Interval.hs" #-}
         (foreveryPair genInterval $ \i j -> not (i `properlyIntersects` j) ==> overlapTime i j == 0)
- DocTest.printPrefix "Data.Interval:231: "
-{-# LINE 231 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:239: "
+{-# LINE 239 "src/Data/Interval.hs" #-}
  DocTest.property
-{-# LINE 231 "src/Data/Interval.hs" #-}
+{-# LINE 239 "src/Data/Interval.hs" #-}
         (foreveryPair genInterval $ \i j -> overlapTime i j == (sum $ fmap intervalDuration $ maybeIntersection i j))
- DocTest.printPrefix "Data.Interval:241: "
-{-# LINE 241 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:249: "
+{-# LINE 249 "src/Data/Interval.hs" #-}
  DocTest.property
-{-# LINE 241 "src/Data/Interval.hs" #-}
+{-# LINE 249 "src/Data/Interval.hs" #-}
         (forevery genInterval $ \i c -> prevailing i (Seq.singleton (c,i)) == Just (c::Char))
- DocTest.printPrefix "Data.Interval:242: "
-{-# LINE 242 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:250: "
+{-# LINE 250 "src/Data/Interval.hs" #-}
  DocTest.property
-{-# LINE 242 "src/Data/Interval.hs" #-}
+{-# LINE 250 "src/Data/Interval.hs" #-}
         (foreveryPairOf genInterval genLabeledSeq $ \i js -> isJust (prevailing i js) == any (intersects i . snd) js)
- DocTest.printPrefix "Data.Interval:243: "
-{-# LINE 243 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:251: "
+{-# LINE 251 "src/Data/Interval.hs" #-}
  DocTest.property
-{-# LINE 243 "src/Data/Interval.hs" #-}
+{-# LINE 251 "src/Data/Interval.hs" #-}
         (forevery genInterval $ \i -> foreveryPair genLabeledSeq $ \js ks -> all (flip elem $ catMaybes [prevailing i js, prevailing i ks]) $ prevailing i (js<>ks))
- DocTest.printPrefix "Data.Interval:266: "
-{-# LINE 266 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:274: "
+{-# LINE 274 "src/Data/Interval.hs" #-}
  DocTest.property
-{-# LINE 266 "src/Data/Interval.hs" #-}
+{-# LINE 274 "src/Data/Interval.hs" #-}
         (foreveryPair genInterval $ \i j -> isJust (maybeUnion i j) ==> fromJust (maybeUnion i j) `contains` i && fromJust (maybeUnion i j) `contains` j)
- DocTest.printPrefix "Data.Interval:267: "
-{-# LINE 267 "src/Data/Interval.hs" #-}
- DocTest.property
-{-# LINE 267 "src/Data/Interval.hs" #-}
-        (foreveryPair genInterval $ \i j -> i `intersects` j ==> (maybeUnion i j >>= maybeIntersection i) == Just i)
  DocTest.printPrefix "Data.Interval:275: "
 {-# LINE 275 "src/Data/Interval.hs" #-}
  DocTest.property
 {-# LINE 275 "src/Data/Interval.hs" #-}
-        (foreveryPair genInterval $ \i j -> i `intersects` j ==> i `contains` fromJust (maybeIntersection i j))
+        (foreveryPair genInterval $ \i j -> i `intersects` j ==> (maybeUnion i j >>= maybeIntersection i) == Just i)
  DocTest.printPrefix "Data.Interval:283: "
 {-# LINE 283 "src/Data/Interval.hs" #-}
  DocTest.property
 {-# LINE 283 "src/Data/Interval.hs" #-}
+        (foreveryPair genInterval $ \i j -> i `intersects` j ==> i `contains` fromJust (maybeIntersection i j))
+ DocTest.printPrefix "Data.Interval:291: "
+{-# LINE 291 "src/Data/Interval.hs" #-}
+ DocTest.property
+{-# LINE 291 "src/Data/Interval.hs" #-}
         (\xs -> isJust (hull xs) ==> all (\x -> fromJust (hull xs) `contains` x) (xs :: [(Int,Int)]))
- DocTest.printPrefix "Data.Interval:300: "
-{-# LINE 300 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:308: "
+{-# LINE 308 "src/Data/Interval.hs" #-}
  DocTest.property
-{-# LINE 300 "src/Data/Interval.hs" #-}
+{-# LINE 308 "src/Data/Interval.hs" #-}
         (foreveryPair genInterval $ \i j -> length (i `without` j) <= 2)
- DocTest.printPrefix "Data.Interval:301: "
-{-# LINE 301 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:309: "
+{-# LINE 309 "src/Data/Interval.hs" #-}
  DocTest.property
-{-# LINE 301 "src/Data/Interval.hs" #-}
+{-# LINE 309 "src/Data/Interval.hs" #-}
         (forevery     genInterval $ \i -> i `without` i == [])
- DocTest.printPrefix "Data.Interval:302: "
-{-# LINE 302 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:310: "
+{-# LINE 310 "src/Data/Interval.hs" #-}
  DocTest.property
-{-# LINE 302 "src/Data/Interval.hs" #-}
+{-# LINE 310 "src/Data/Interval.hs" #-}
         (foreveryPair genInterval $ \i j -> all (contains i) (i `without` j))
- DocTest.printPrefix "Data.Interval:303: "
-{-# LINE 303 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:311: "
+{-# LINE 311 "src/Data/Interval.hs" #-}
  DocTest.property
-{-# LINE 303 "src/Data/Interval.hs" #-}
+{-# LINE 311 "src/Data/Interval.hs" #-}
         (foreveryPair genInterval $ \i j -> not $ any (properlyIntersects j) (i `without` j))
- DocTest.printPrefix "Data.Interval:291: "
-{-# LINE 291 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:299: "
+{-# LINE 299 "src/Data/Interval.hs" #-}
  DocTest.example
-{-# LINE 291 "src/Data/Interval.hs" #-}
+{-# LINE 299 "src/Data/Interval.hs" #-}
       (without' (1,5) (4,5))
   [ExpectedLine [LineChunk "[(1,4)]"]]
- DocTest.printPrefix "Data.Interval:293: "
-{-# LINE 293 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:301: "
+{-# LINE 301 "src/Data/Interval.hs" #-}
  DocTest.example
-{-# LINE 293 "src/Data/Interval.hs" #-}
+{-# LINE 301 "src/Data/Interval.hs" #-}
       (without' (1,5) (2,3))
   [ExpectedLine [LineChunk "[(1,2),(3,5)]"]]
- DocTest.printPrefix "Data.Interval:295: "
-{-# LINE 295 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:303: "
+{-# LINE 303 "src/Data/Interval.hs" #-}
  DocTest.example
-{-# LINE 295 "src/Data/Interval.hs" #-}
+{-# LINE 303 "src/Data/Interval.hs" #-}
       (without' (1,5) (1,5))
   [ExpectedLine [LineChunk "[]"]]
- DocTest.printPrefix "Data.Interval:297: "
-{-# LINE 297 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:305: "
+{-# LINE 305 "src/Data/Interval.hs" #-}
  DocTest.example
-{-# LINE 297 "src/Data/Interval.hs" #-}
+{-# LINE 305 "src/Data/Interval.hs" #-}
       (without' (1,5) (0,1))
   [ExpectedLine [LineChunk "[(1,5)]"]]
- DocTest.printPrefix "Data.Interval:319: "
-{-# LINE 319 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:327: "
+{-# LINE 327 "src/Data/Interval.hs" #-}
  DocTest.property
-{-# LINE 319 "src/Data/Interval.hs" #-}
+{-# LINE 327 "src/Data/Interval.hs" #-}
         (forevery genSortedIntervals $ all (\xs -> and $ List.zipWith intersects xs (tail xs)) . contiguous)
- DocTest.printPrefix "Data.Interval:320: "
-{-# LINE 320 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:328: "
+{-# LINE 328 "src/Data/Interval.hs" #-}
  DocTest.property
-{-# LINE 320 "src/Data/Interval.hs" #-}
+{-# LINE 328 "src/Data/Interval.hs" #-}
         (forevery genSortedIntervals $ all ((1==).length.components) . contiguous)
- DocTest.printPrefix "Data.Interval:335: "
-{-# LINE 335 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:343: "
+{-# LINE 343 "src/Data/Interval.hs" #-}
  DocTest.property
-{-# LINE 335 "src/Data/Interval.hs" #-}
+{-# LINE 343 "src/Data/Interval.hs" #-}
         (forevery genSortedIntervals $ \xs -> all (\i -> any (flip contains i) (components xs)) xs)
- DocTest.printPrefix "Data.Interval:336: "
-{-# LINE 336 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:344: "
+{-# LINE 344 "src/Data/Interval.hs" #-}
  DocTest.property
-{-# LINE 336 "src/Data/Interval.hs" #-}
+{-# LINE 344 "src/Data/Interval.hs" #-}
         (forevery genSortedIntervals $ \xs -> let cs = components xs in all (\(i,j) -> i == j || not (i `intersects` j)) [(c1,c2) | c1 <- cs, c2 <- cs])
- DocTest.printPrefix "Data.Interval:355: "
-{-# LINE 355 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:363: "
+{-# LINE 363 "src/Data/Interval.hs" #-}
  DocTest.property
-{-# LINE 355 "src/Data/Interval.hs" #-}
+{-# LINE 363 "src/Data/Interval.hs" #-}
         (forevery genSortedIntervals   $ \xs -> componentsSeq (Seq.fromList xs) == Seq.fromList (components xs))
- DocTest.printPrefix "Data.Interval:356: "
-{-# LINE 356 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:364: "
+{-# LINE 364 "src/Data/Interval.hs" #-}
  DocTest.property
-{-# LINE 356 "src/Data/Interval.hs" #-}
+{-# LINE 364 "src/Data/Interval.hs" #-}
         (forevery genSortedIntervalSeq $ \xs -> let cs = componentsSeq xs in all (\(i,j) -> i == j || not (i `intersects` j)) $ do {c1 <- cs; c2 <- cs; return (c1,c2)})
- DocTest.printPrefix "Data.Interval:369: "
-{-# LINE 369 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:377: "
+{-# LINE 377 "src/Data/Interval.hs" #-}
  DocTest.property
-{-# LINE 369 "src/Data/Interval.hs" #-}
+{-# LINE 377 "src/Data/Interval.hs" #-}
         (foreveryPairOf genInterval genIntervalSeq $ \i js -> all (contains i) (covered i js))
- DocTest.printPrefix "Data.Interval:370: "
-{-# LINE 370 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:378: "
+{-# LINE 378 "src/Data/Interval.hs" #-}
  DocTest.property
-{-# LINE 370 "src/Data/Interval.hs" #-}
+{-# LINE 378 "src/Data/Interval.hs" #-}
         (foreveryPairOf genInterval genIntervalSeq $ \i js -> covered i (covered i js) == covered i js)
- DocTest.printPrefix "Data.Interval:376: "
-{-# LINE 376 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:384: "
+{-# LINE 384 "src/Data/Interval.hs" #-}
  DocTest.property
-{-# LINE 376 "src/Data/Interval.hs" #-}
+{-# LINE 384 "src/Data/Interval.hs" #-}
         (foreveryPair   genInterval $ \i j -> j `contains` i == i `coveredBy` [j])
- DocTest.printPrefix "Data.Interval:377: "
-{-# LINE 377 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:385: "
+{-# LINE 385 "src/Data/Interval.hs" #-}
  DocTest.property
-{-# LINE 377 "src/Data/Interval.hs" #-}
+{-# LINE 385 "src/Data/Interval.hs" #-}
         (foreveryPairOf genInterval genSortedIntervals $ \i js -> i `coveredBy` js ==> any (flip contains i) (components js))
- DocTest.printPrefix "Data.Interval:383: "
-{-# LINE 383 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:391: "
+{-# LINE 391 "src/Data/Interval.hs" #-}
  DocTest.property
-{-# LINE 383 "src/Data/Interval.hs" #-}
+{-# LINE 391 "src/Data/Interval.hs" #-}
         (foreveryPairOf genNonEmptyInterval genIntervalSeq         $ \i js -> i `coveredBy` js == (fractionCovered i js >= (1::Rational)))
- DocTest.printPrefix "Data.Interval:384: "
-{-# LINE 384 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:392: "
+{-# LINE 392 "src/Data/Interval.hs" #-}
  DocTest.property
-{-# LINE 384 "src/Data/Interval.hs" #-}
+{-# LINE 392 "src/Data/Interval.hs" #-}
         (foreveryPairOf genNonEmptyInterval genNonEmptyIntervalSeq $ \i js -> any (properlyIntersects i) js == (fractionCovered i js > (0::Rational)))
- DocTest.printPrefix "Data.Interval:403: "
-{-# LINE 403 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:411: "
+{-# LINE 411 "src/Data/Interval.hs" #-}
  DocTest.property
-{-# LINE 403 "src/Data/Interval.hs" #-}
+{-# LINE 411 "src/Data/Interval.hs" #-}
         (foreveryPair genInterval $ \i j -> i `intersects` j  ==  (overlap i j == EQ))
- DocTest.printPrefix "Data.Interval:421: "
-{-# LINE 421 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:429: "
+{-# LINE 429 "src/Data/Interval.hs" #-}
  DocTest.property
-{-# LINE 421 "src/Data/Interval.hs" #-}
+{-# LINE 429 "src/Data/Interval.hs" #-}
         (foreveryPair genInterval $ \i j -> i `properlyIntersects` j  ==  (properOverlap i j == EQ))
- DocTest.printPrefix "Data.Interval:433: "
-{-# LINE 433 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:441: "
+{-# LINE 441 "src/Data/Interval.hs" #-}
  DocTest.property
-{-# LINE 433 "src/Data/Interval.hs" #-}
+{-# LINE 441 "src/Data/Interval.hs" #-}
         (foreveryPair genInterval $ \i j -> (lb i <= ub i && lb j <= ub j && i `intersects` j)  ==  (max (lb i) (lb j) <= min (ub i) (ub j)))
- DocTest.printPrefix "Data.Interval:430: "
-{-# LINE 430 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:438: "
+{-# LINE 438 "src/Data/Interval.hs" #-}
  DocTest.example
-{-# LINE 430 "src/Data/Interval.hs" #-}
+{-# LINE 438 "src/Data/Interval.hs" #-}
       (((1,2)::(Int,Int)) `intersects` ((2,3)::(Int,Int)))
   [ExpectedLine [LineChunk "True"]]
- DocTest.printPrefix "Data.Interval:444: "
-{-# LINE 444 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:452: "
+{-# LINE 452 "src/Data/Interval.hs" #-}
  DocTest.property
-{-# LINE 444 "src/Data/Interval.hs" #-}
+{-# LINE 452 "src/Data/Interval.hs" #-}
         (foreveryPair genInterval $ \i j -> ((i `intersects` j) && not (i `properlyIntersects` j))  ==  (ub i == lb j || ub j == lb i))
- DocTest.printPrefix "Data.Interval:450: "
-{-# LINE 450 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:458: "
+{-# LINE 458 "src/Data/Interval.hs" #-}
  DocTest.property
-{-# LINE 450 "src/Data/Interval.hs" #-}
+{-# LINE 458 "src/Data/Interval.hs" #-}
         (forevery     genInterval $ \i -> i `contains` i)
- DocTest.printPrefix "Data.Interval:451: "
-{-# LINE 451 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:459: "
+{-# LINE 459 "src/Data/Interval.hs" #-}
  DocTest.property
-{-# LINE 451 "src/Data/Interval.hs" #-}
+{-# LINE 459 "src/Data/Interval.hs" #-}
         (foreveryPair genInterval $ \i j -> (i `contains` j && j `contains` i) == (i==j))
- DocTest.printPrefix "Data.Interval:452: "
-{-# LINE 452 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:460: "
+{-# LINE 460 "src/Data/Interval.hs" #-}
  DocTest.property
-{-# LINE 452 "src/Data/Interval.hs" #-}
+{-# LINE 460 "src/Data/Interval.hs" #-}
         (foreveryPair genInterval $ \i j -> i `contains` j == (maybeUnion i j == Just i))
- DocTest.printPrefix "Data.Interval:464: "
-{-# LINE 464 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:472: "
+{-# LINE 472 "src/Data/Interval.hs" #-}
  DocTest.property
-{-# LINE 464 "src/Data/Interval.hs" #-}
+{-# LINE 472 "src/Data/Interval.hs" #-}
         (forevery genSortedList $ \xs -> (components $ toList $ fromEndPoints xs) == if length xs < 2 then [] else [(head xs, last xs)])
- DocTest.printPrefix "Data.Interval:465: "
-{-# LINE 465 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:473: "
+{-# LINE 473 "src/Data/Interval.hs" #-}
  DocTest.property
-{-# LINE 465 "src/Data/Interval.hs" #-}
+{-# LINE 473 "src/Data/Interval.hs" #-}
         (forevery genSortedList $ \xs -> hullSeqNonNested (fromEndPoints xs) == if length xs < 2 then Nothing else Just (head xs,last xs))
- DocTest.printPrefix "Data.Interval:478: "
-{-# LINE 478 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:487: "
+{-# LINE 487 "src/Data/Interval.hs" #-}
  DocTest.property
-{-# LINE 478 "src/Data/Interval.hs" #-}
-        (foreveryPairOf genInterval genSortedIntervalSeq $ \i js -> toList (getIntersects i (FromSortedSeq js)) `List.isSubsequenceOf` toList js)
- DocTest.printPrefix "Data.Interval:479: "
-{-# LINE 479 "src/Data/Interval.hs" #-}
+{-# LINE 487 "src/Data/Interval.hs" #-}
+        (foreveryPairOf genInterval genNonNestedIntervalSeq $ \i js -> toList (getIntersects i (FromSortedSeq js)) `isSubsequenceOf` toList js)
+ DocTest.printPrefix "Data.Interval:488: "
+{-# LINE 488 "src/Data/Interval.hs" #-}
  DocTest.property
-{-# LINE 479 "src/Data/Interval.hs" #-}
+{-# LINE 488 "src/Data/Interval.hs" #-}
         (forevery genSortedIntervalSeq $ \xs -> propSplit (\subseq -> subseq == sortByRight subseq) (splitSeq xs))
- DocTest.printPrefix "Data.Interval:496: "
-{-# LINE 496 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:505: "
+{-# LINE 505 "src/Data/Interval.hs" #-}
  DocTest.property
-{-# LINE 496 "src/Data/Interval.hs" #-}
+{-# LINE 505 "src/Data/Interval.hs" #-}
         (forevery genSortedIntervalSeq $ \xs -> hullSeq xs == if Seq.null xs then Nothing else Just (minimum (fmap lb xs),maximum (fmap ub xs)))
- DocTest.printPrefix "Data.Interval:497: "
-{-# LINE 497 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:506: "
+{-# LINE 506 "src/Data/Interval.hs" #-}
  DocTest.property
-{-# LINE 497 "src/Data/Interval.hs" #-}
+{-# LINE 506 "src/Data/Interval.hs" #-}
         (forevery genSortedIntervalSeq $ \xs -> hullSeq xs == hull (toList xs))
- DocTest.printPrefix "Data.Interval:516: "
-{-# LINE 516 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:525: "
+{-# LINE 525 "src/Data/Interval.hs" #-}
  DocTest.property
-{-# LINE 516 "src/Data/Interval.hs" #-}
+{-# LINE 525 "src/Data/Interval.hs" #-}
         (foreveryPairOf genInterval genNonNestedIntervalSeq $ \i js' -> let js = toList js' in fst (splitIntersecting i js) == filter (intersects i) js)
- DocTest.printPrefix "Data.Interval:517: "
-{-# LINE 517 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:526: "
+{-# LINE 526 "src/Data/Interval.hs" #-}
  DocTest.property
-{-# LINE 517 "src/Data/Interval.hs" #-}
+{-# LINE 526 "src/Data/Interval.hs" #-}
         (foreveryPairOf genInterval genNonNestedIntervalSeq $ \i js' -> let js = toList js' in all (\j -> not (ub j < ub i)) (snd (splitIntersecting i js)))
- DocTest.printPrefix "Data.Interval:513: "
-{-# LINE 513 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:522: "
+{-# LINE 522 "src/Data/Interval.hs" #-}
  DocTest.example
-{-# LINE 513 "src/Data/Interval.hs" #-}
+{-# LINE 522 "src/Data/Interval.hs" #-}
       (splitIntersecting ((2,5) :: (Int,Int)) ([(0,1),(2,2),(2,3),(3,6),(6,7)] :: [(Int,Int)]))
   [ExpectedLine [LineChunk "([(2,2),(2,3),(3,6)],[(3,6),(6,7)])"]]
- DocTest.printPrefix "Data.Interval:537: "
-{-# LINE 537 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:546: "
+{-# LINE 546 "src/Data/Interval.hs" #-}
  DocTest.property
-{-# LINE 537 "src/Data/Interval.hs" #-}
+{-# LINE 546 "src/Data/Interval.hs" #-}
         (foreveryPairOf genInterval genNonNestedIntervalSeq $ \i js' -> let js = toList js' in fst (splitProperlyIntersecting i js) == filter (properlyIntersects i) js)
- DocTest.printPrefix "Data.Interval:538: "
-{-# LINE 538 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:547: "
+{-# LINE 547 "src/Data/Interval.hs" #-}
  DocTest.property
-{-# LINE 538 "src/Data/Interval.hs" #-}
+{-# LINE 547 "src/Data/Interval.hs" #-}
         (foreveryPairOf genInterval genNonNestedIntervalSeq $ \i js' -> let js = toList js' in all (not.properlyContains i) (snd (splitProperlyIntersecting i js)))
- DocTest.printPrefix "Data.Interval:534: "
-{-# LINE 534 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:543: "
+{-# LINE 543 "src/Data/Interval.hs" #-}
  DocTest.example
-{-# LINE 534 "src/Data/Interval.hs" #-}
+{-# LINE 543 "src/Data/Interval.hs" #-}
       (splitProperlyIntersecting ((2,5) :: (Int,Int))  ([(0,1),(2,3),(2,2),(3,5),(5,6),(6,7)] :: [(Int,Int)]))
   [ExpectedLine [LineChunk "([(2,3),(3,5)],[(5,6),(6,7)])"]]
- DocTest.printPrefix "Data.Interval:570: "
-{-# LINE 570 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:579: "
+{-# LINE 579 "src/Data/Interval.hs" #-}
  DocTest.property
-{-# LINE 570 "src/Data/Interval.hs" #-}
+{-# LINE 579 "src/Data/Interval.hs" #-}
         (forevery genSortedIntervalSeq $ \xs -> hullSeq xs == hullOfTree (itree 4 xs))
- DocTest.printPrefix "Data.Interval:581: "
-{-# LINE 581 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:590: "
+{-# LINE 590 "src/Data/Interval.hs" #-}
  DocTest.property
-{-# LINE 581 "src/Data/Interval.hs" #-}
+{-# LINE 590 "src/Data/Interval.hs" #-}
         (forevery genIntervalSeq $ \xs -> invariant . itree 4 $ xs)
- DocTest.printPrefix "Data.Interval:591: "
-{-# LINE 591 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:600: "
+{-# LINE 600 "src/Data/Interval.hs" #-}
  DocTest.property
-{-# LINE 591 "src/Data/Interval.hs" #-}
+{-# LINE 600 "src/Data/Interval.hs" #-}
         (foreveryPairOf genInterval genIntervalSeq $ \i t -> on (==) sortByRight (getIntersects i $ itree 2 t) (i `intersecting` t))
- DocTest.printPrefix "Data.Interval:602: "
-{-# LINE 602 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:611: "
+{-# LINE 611 "src/Data/Interval.hs" #-}
  DocTest.property
-{-# LINE 602 "src/Data/Interval.hs" #-}
+{-# LINE 611 "src/Data/Interval.hs" #-}
         (foreveryPairOf genInterval genIntervalSeq $ \i t -> on (==) sortByRight (getProperIntersects i $ itree 2 t) (i `intersectingProperly` t))
- DocTest.printPrefix "Data.Interval:734: "
-{-# LINE 734 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:743: "
+{-# LINE 743 "src/Data/Interval.hs" #-}
  DocTest.property
-{-# LINE 734 "src/Data/Interval.hs" #-}
+{-# LINE 743 "src/Data/Interval.hs" #-}
         (forevery genIntervalSeq $ \is -> joinSeq (splitSeq is) == is)
- DocTest.printPrefix "Data.Interval:796: "
-{-# LINE 796 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:805: "
+{-# LINE 805 "src/Data/Interval.hs" #-}
  DocTest.property
-{-# LINE 796 "src/Data/Interval.hs" #-}
+{-# LINE 805 "src/Data/Interval.hs" #-}
         (forevery genNonNestedIntervalSeq $ \xs -> hullSeqNonNested xs == hullSeq xs)
- DocTest.printPrefix "Data.Interval:813: "
-{-# LINE 813 "src/Data/Interval.hs" #-}
+ DocTest.printPrefix "Data.Interval:822: "
+{-# LINE 822 "src/Data/Interval.hs" #-}
  DocTest.property
-{-# LINE 813 "src/Data/Interval.hs" #-}
+{-# LINE 822 "src/Data/Interval.hs" #-}
         (foreveryPairOf genInterval genNonNestedIntervalSeq $ \i js -> getIntersects i (FromSortedSeq js) == intersecting i js)
diff --git a/src/Data/Interval.hs b/src/Data/Interval.hs
--- a/src/Data/Interval.hs
+++ b/src/Data/Interval.hs
@@ -115,6 +115,7 @@
 -- >>> import Data.Foldable (toList)
 -- >>> import Test.QuickCheck ((==>))
 -- >>> without' :: (Int,Int) -> (Int,Int) -> [(Int,Int)]; without' = without
+-- >>> isSubsequenceOf :: Eq a => [a] -> [a] -> Bool; isSubsequenceOf [] _ = True; isSubsequenceOf (_:_) [] = False; isSubsequenceOf xs@(x:xs') (y:ys) = (x == y && xs' `List.isPrefixOf` ys) || xs `isSubsequenceOf` ys
 
 
 -- | class of intervals with end points in a totally ordered type
@@ -177,6 +178,13 @@
 -- False
 --
 -- Thus, when querying against a set of intervals with nesting, you must use an 'ITree' instead. 
+-- Observe that non-nestedness is a quite strong property. 
+-- The logical negation of the sentence /there exist intervals i, j such that i is contained in j/
+-- is /for all i, j either/ @lb i < lb j@ or @ub i > ub j@. 
+-- But if @lb i < lb j@ then also @ub i < ub j@ because otherwise i contains j. 
+-- Likewise, @ub i > ub j@ implies @lb i > lb j@ otherwise i contains j. 
+-- Hence a non-nested sequence of intervals can be sorted by either left of right end-point 
+-- resulting in the same order. 
 --
 -- prop> forevery genNonNestedIntervalSeq $ \xs -> propSplit (\subseq -> hullSeqNonNested subseq == hullSeq subseq) (splitSeq xs) 
 newtype NonNestedSeq a = FromSortedSeq {getSeq :: Seq a} deriving (Eq,Ord,Show,Functor,Foldable,Traversable)
@@ -472,10 +480,11 @@
     EmptyL     -> error "Intervals.fromEndPoints: this should never happen"
 
 -- | lexicographical sort by 'ub', then inverse 'lb'.
--- In the resulting list, the intervals intersecting
+-- If the sequence of intervals is non-nested, then 
+-- in the resulting list the intervals intersecting
 -- a given interval form a contiguous sublist.
 --
--- prop> foreveryPairOf genInterval genSortedIntervalSeq $ \i js -> toList (getIntersects i (FromSortedSeq js)) `List.isSubsequenceOf` toList js
+-- prop> foreveryPairOf genInterval genNonNestedIntervalSeq $ \i js -> toList (getIntersects i (FromSortedSeq js)) `isSubsequenceOf` toList js
 -- prop> forevery genSortedIntervalSeq $ \xs -> propSplit (\subseq -> subseq == sortByRight subseq) (splitSeq xs)
 sortByRight :: (Interval e i) => Seq i -> Seq i
 sortByRight = Seq.sortBy (\i j -> compare (ub i) (ub j) <> compare (lb j) (lb i))
diff --git a/test/Data/IntervalTest.hs b/test/Data/IntervalTest.hs
--- a/test/Data/IntervalTest.hs
+++ b/test/Data/IntervalTest.hs
@@ -19,7 +19,7 @@
 import qualified Data.Sequence as Seq
 import qualified Data.List as List
 import Data.Foldable (toList)
-import Data.Sequence (Seq)
+import Data.Sequence (Seq,(|>))
 import Data.Time (UTCTime)
 
 import Control.Arrow (first)
@@ -89,14 +89,22 @@
 genIntervalSeq =
     withShrinkSeq $ fmap Seq.fromList $ QC.listOf $ fst genInterval
 
--- | generate a Sequence of non-nested intervals by means of 'fromEndPoints'
+-- | For @i :: Intv@ generates @j@ such that 
+-- @lb i < lb j@ and @ub i < ub j@ 
+genNextIntv :: Intv -> QC.Gen Intv
+genNextIntv i = do
+    x <- genUTCTime `QC.suchThat` ((lb i)<)
+    y <- genUTCTime `QC.suchThat` ((max x (ub i))<)
+    return (x,y)
+
+-- | generate a Sequence of non-nested intervals
 genNonNestedIntervalSeq :: Gen (Seq Intv)
-genNonNestedIntervalSeq =
-    withShrinkSeq $
-    filterM (const QC.arbitrary) . fromEndPoints . List.sort
-        =<< QC.listOf genUTCTime
--- TODO: these are also non-properly-overlapping, but we wish to include 
--- non-containment overlaps in the tests.
+genNonNestedIntervalSeq = withShrinkSeq $ fst genInterval >>= go mempty where
+    go js j = do
+        done <- QC.arbitrary
+        if done then return js else do
+            i <- genNextIntv j
+            go (js |> j) i
 
 genNonEmptyIntervalSeq :: Gen (Seq Intv)
 genNonEmptyIntervalSeq =