diff --git a/Changelog.md b/Changelog.md
--- a/Changelog.md
+++ b/Changelog.md
@@ -1,15 +1,19 @@
-Changes in version 0.2.0
-
-* Better performance!
-* Major bump because of strictness changes.
-* Functions are now slightly stricter.
-  In the past the successor list of nodes unreachable from the root wasn't evaluated.
-  This is no longer the case and they will be evaluated.
-  Moving forward users should expect all inputs to be evaluated unless stated otherwise.
-* Requires GHC >= 8.0 to build (base dependency)
-* Requires containers >= 0.5
-* Exchanged the deprecated container functions with their replacements.
-* Replaced a few right folds with strict left folds.
-* Commented out/removed some unused code.
-* Replaced mapsnd and swap with variants from base.
+## Changes in version 0.2.1
+
+* Fixed a bug that resulted in incorrect results.
+
+## Changes in version 0.2.0
+
+* Better performance!
+* Major bump because of strictness changes.
+* Functions are now slightly stricter.
+  In the past the successor list of nodes unreachable from the root wasn't evaluated.
+  This is no longer the case and they will be evaluated.
+  Moving forward users should expect all inputs to be evaluated unless stated otherwise.
+* Requires GHC >= 8.0 to build (base dependency)
+* Requires containers >= 0.5
+* Exchanged the deprecated container functions with their replacements.
+* Replaced a few right folds with strict left folds.
+* Commented out/removed some unused code.
+* Replaced mapsnd and swap with variants from base.
 * Add very simplistic benchmark/test suites.
diff --git a/Data/Graph/Dom.hs b/Data/Graph/Dom.hs
--- a/Data/Graph/Dom.hs
+++ b/Data/Graph/Dom.hs
@@ -459,14 +459,23 @@
 predG :: Graph -> Graph
 predG g = IM.unionWith IS.union (go g) g0
   where g0 = fmap (const mempty) g
-        f :: IntMap IntSet -> Int -> IntSet -> IntMap IntSet
-        f m i a = foldl' (\m p -> IM.insertWith mappend p
+        go = flip IM.foldrWithKey mempty (\i a m ->
+                foldl' (\m p -> IM.insertWith mappend p
                                       (IS.singleton i) m)
                         m
-                       (IS.toList a)
-        go :: IntMap IntSet -> IntMap IntSet
-        go = flip IM.foldlWithKey' mempty f
+                       (IS.toList a))
 
+-- predG :: Graph -> Graph
+-- predG g = IM.unionWith IS.union (go g) g0
+--   where g0 = fmap (const mempty) g
+--         f :: IntMap IntSet -> Int -> IntSet -> IntMap IntSet
+--         f m i a = foldl' (\m p -> IM.insertWith mappend p
+--                                       (IS.singleton i) m)
+--                         m
+--                        (IS.toList a)
+--         go :: IntMap IntSet -> IntMap IntSet
+--         go = flip IM.foldlWithKey' mempty f
+
 pruneReach :: Rooted -> Rooted
 pruneReach (r,g) = (r,g2)
   where is = reachable
@@ -525,28 +534,24 @@
 -- (renamed, old -> new)
 renum :: Int -> Graph -> (Graph, NodeMap Node)
 renum from = (\(_,m,g)->(g,m))
-  . IM.foldlWithKey'
-      f (from,mempty,mempty)
-  where
-    f :: (Int, NodeMap Node, IntMap IntSet) -> Node -> IntSet
-      -> (Int, NodeMap Node, IntMap IntSet)
-    f (!n,!env,!new) i ss =
-            let (j,n2,env2) = go n env i
-                (n3,env3,ss2) = IS.fold
-                  (\k (!n,!env,!new)->
-                      case go n env k of
-                        (l,n2,env2)-> (n2,env2,l `IS.insert` new))
-                  (n2,env2,mempty) ss
-                new2 = IM.insertWith IS.union j ss2 new
-            in (n3,env3,new2)
-    go :: Int
-        -> NodeMap Node
-        -> Node
-        -> (Node,Int,NodeMap Node)
-    go !n !env i =
-        case IM.lookup i env of
-        Just j -> (j,n,env)
-        Nothing -> (n,n+1,IM.insert i n env)
+  . IM.foldrWithKey
+      (\i ss (!n,!env,!new)->
+          let (j,n2,env2) = go n env i
+              (n3,env3,ss2) = IS.fold
+                (\k (!n,!env,!new)->
+                    case go n env k of
+                      (l,n2,env2)-> (n2,env2,l `IS.insert` new))
+                (n2,env2,mempty) ss
+              new2 = IM.insertWith IS.union j ss2 new
+          in (n3,env3,new2)) (from,mempty,mempty)
+  where go :: Int
+           -> NodeMap Node
+           -> Node
+           -> (Node,Int,NodeMap Node)
+        go !n !env i =
+          case IM.lookup i env of
+            Just j -> (j,n,env)
+            Nothing -> (n,n+1,IM.insert i n env)
 
 -----------------------------------------------------------------------------
 
@@ -554,10 +559,10 @@
 instance Functor (S z s) where
   fmap f (S g) = S (\k -> g (k . f))
 instance Monad (S z s) where
-  return a = S (\k -> k a)
+  return = pure
   S g >>= f = S (\k -> g (\a -> unS (f a) k))
 instance Applicative (S z s) where
-  pure = return
+  pure a = S (\k -> k a)
   (<*>) = ap
 -- get :: S z s s
 -- get = S (\k s -> k s s)
diff --git a/Setup.lhs b/Setup.lhs
--- a/Setup.lhs
+++ b/Setup.lhs
@@ -1,3 +1,3 @@
-> import Distribution.Simple
-> main :: IO ()
+> import Distribution.Simple
+> main :: IO ()
 > main = defaultMain
diff --git a/dom-lt.cabal b/dom-lt.cabal
--- a/dom-lt.cabal
+++ b/dom-lt.cabal
@@ -1,60 +1,68 @@
-name:               dom-lt
-version:            0.2.0
-cabal-version:      >= 1.10
-build-type:         Simple
-license:            BSD3
-license-file:       LICENSE
-category:           Algorithms, Graphs
-author:             Matt Morrow
-copyright:          (c) Matt Morrow, 2009
-maintainer:         Andreas Klebinger <klebinger.andreas@gmx.at>
-bug-reports:        https://github.com/AndreasPK/dom-lt/issues
-stability:          stable
-synopsis:           The Lengauer-Tarjan graph dominators algorithm.
-description:
-    The Lengauer-Tarjan graph dominators algorithm.
-
-    Included are ways to compute domination and post-domination relationships.
-
-Extra-Source-Files:
-  Changelog.md
-
-source-repository head
-  type: git
-  location: https://github.com/AndreasPK/dom-lt
-
-library
-  Default-Language: Haskell2010
-  includes:
-  build-tools:
-  extra-libraries:
-  hs-source-dirs:   .
-  ghc-options:      -O2 -funbox-strict-fields
-  default-extensions: RankNTypes
-  build-depends:    base >= 4.9 && < 5, array, containers >= 0.5
-  exposed-modules:  Data.Graph.Dom
-
-test-suite dom-lt-tests
-  Default-Language: Haskell2010
-  type: exitcode-stdio-1.0
-
-  Main-Is:  Main.hs
-  hs-source-dirs: tests
-
-  Build-Depends: base, dom-lt, containers
-
-  default-extensions:
-  Ghc-Options: -Wall
-
-benchmark dom-lt-bench
-  Default-Language: Haskell2010
-  type: exitcode-stdio-1.0
-
-  Main-Is:  Main.hs
-  hs-source-dirs: benchmarks
-
-  Build-Depends: base, dom-lt, containers, criterion >= 1.4, deepseq
-  default-extensions:
-
-  Ghc-Options: -O2 -fno-full-laziness
-
+name:               dom-lt
+version:            0.2.1
+cabal-version:      >= 1.10
+build-type:         Simple
+tested-with:        GHC == 8.10.1 || == 8.8.4 || == 8.0.1
+license:            BSD3
+license-file:       LICENSE
+category:           Algorithms, Graphs
+author:             Matt Morrow
+copyright:          (c) Matt Morrow, 2009
+maintainer:         Andreas Klebinger <klebinger.andreas@gmx.at>
+bug-reports:        https://github.com/AndreasPK/dom-lt/issues
+stability:          stable
+synopsis:           The Lengauer-Tarjan graph dominators algorithm.
+description:
+    The Lengauer-Tarjan graph dominators algorithm.
+
+    Included are ways to compute domination and post-domination relationships.
+
+Extra-Source-Files:
+  Changelog.md
+
+source-repository head
+  type: git
+  location: https://github.com/AndreasPK/dom-lt
+
+library
+  Default-Language: Haskell2010
+  includes:
+  build-tools:
+  extra-libraries:
+  hs-source-dirs:   .
+  ghc-options:      -O2 -funbox-strict-fields
+  default-extensions: RankNTypes
+  build-depends:
+      base >= 4.9 && < 5
+    , array
+    , containers >= 0.5 && < 0.7
+  exposed-modules:  Data.Graph.Dom
+
+test-suite dom-lt-tests
+  Default-Language: Haskell2010
+  type: exitcode-stdio-1.0
+
+  Main-Is:  Main.hs
+  hs-source-dirs: tests
+
+  build-depends:
+      base                        >=4.6   && <5
+    , dom-lt
+    , containers
+    , HUnit                       >=1.3   && <1.7
+
+  default-extensions:
+  Ghc-Options: -Wall
+
+benchmark dom-lt-bench
+  Default-Language: Haskell2010
+  type: exitcode-stdio-1.0
+
+  Main-Is:  Main.hs
+  hs-source-dirs: benchmarks
+
+  Build-Depends: base, dom-lt, containers, criterion >= 1.4, deepseq
+  default-extensions:
+
+  Ghc-Options: -O2 -fno-full-laziness
+
diff --git a/tests/Main.hs b/tests/Main.hs
--- a/tests/Main.hs
+++ b/tests/Main.hs
@@ -1,61 +1,135 @@
-module Main (main) where
-
-import Data.Graph.Dom as G
-import Data.Tree
-import System.Exit
-
-g0 :: Graph
-g0 = fromAdj
-  [(1,[2,3])
-  ,(2,[3])
-  ,(3,[4])
-  ,(4,[3,5,6])
-  ,(5,[7])
-  ,(6,[7])
-  ,(7,[4,8])
-  ,(8,[3,9,10])
-  ,(9,[1])
-  ,(10,[7])]
-
-g1 :: Graph
-g1 = fromAdj
-  [(0,[1])
-  ,(1,[2,3])
-  ,(2,[7])
-  ,(3,[4])
-  ,(4,[5,6])
-  ,(5,[7])
-  ,(6,[4])
-  ,(7,[])]
-
-applyDomFunctions :: Rooted
-                  -> ([(Node, Path)], [(Node, Path)], [(Node, Node)], [(Node, Node)], Tree Node, Tree Node)
-applyDomFunctions g = (dom g, pdom g, idom g, ipdom g, domTree g, pdomTree g)
-
-g0_expected :: ([(Node, Path)], [(Node, Path)], [(Node, Node)], [(Node, Node)], Tree Node, Tree Node)
-g0_expected = (
-  [(2,[1]),(3,[1]),(4,[3,1]),(5,[4,3,1]),(6,[4,3,1]),(7,[4,3,1]),(8,[7,4,3,1]),(9,[8,7,4,3,1]),(10,[8,7,4,3,1])],
-  [(9,[1]),(8,[9,1]),(7,[8,9,1]),(4,[7,8,9,1]),(5,[7,8,9,1]),(6,[7,8,9,1]),(10,[7,8,9,1]),(3,[4,7,8,9,1]),(2,[3,4,7,8,9,1])],
-  [(10,8),(7,4),(9,8),(1,1),(8,7),(3,1),(4,3),(6,4),(5,4),(2,1)],
-  [(10,7),(8,9),(9,1),(7,8),(6,7),(5,7),(4,7),(3,4),(2,3),(1,1)],
-  Node {rootLabel = 1, subForest = [Node {rootLabel = 2, subForest = []},Node {rootLabel = 3, subForest = [Node {rootLabel = 4, subForest = [Node {rootLabel = 5, subForest = []},Node {rootLabel = 6, subForest = []},Node {rootLabel = 7, subForest = [Node {rootLabel = 8, subForest = [Node {rootLabel = 9, subForest = []},Node {rootLabel = 10, subForest = []}]}]}]}]}]},
-  Node {rootLabel = 1, subForest = [Node {rootLabel = 9, subForest = [Node {rootLabel = 8, subForest = [Node {rootLabel = 7, subForest = [Node {rootLabel = 4, subForest = [Node {rootLabel = 3, subForest = [Node {rootLabel = 2, subForest = []}]}]},Node {rootLabel = 5, subForest = []},Node {rootLabel = 6, subForest = []},Node {rootLabel = 10, subForest = []}]}]}]}]}
-  )
-
-g1_expected :: ([(Node, Path)], [(Node, Path)], [(Node, Node)], [(Node, Node)], Tree Node, Tree Node)
-g1_expected = (
-    [(1,[0]),(2,[1,0]),(3,[1,0]),(7,[1,0]),(4,[3,1,0]),(5,[4,3,1,0]),(6,[4,3,1,0])],
-    [],[(7,1),(6,4),(4,3),(5,4),(3,1),(2,1),(1,0),(0,0)],[(0,0)],
-    Node {rootLabel = 0, subForest = [Node {rootLabel = 1, subForest = [Node {rootLabel = 2, subForest = []},Node {rootLabel = 3, subForest = [Node {rootLabel = 4, subForest = [Node {rootLabel = 5, subForest = []},Node {rootLabel = 6, subForest = []}]}]},
-    Node {rootLabel = 7, subForest = []}]}]},Node {rootLabel = 0, subForest = []})
-
-main :: IO ()
-main = do
-    let g0_result = applyDomFunctions (1,g0)
-    let g1_result = applyDomFunctions (0,g1)
-    if g0_result == g0_expected && g1_result == g1_expected
-        then exitWith ExitSuccess
-        else exitWith $ ExitFailure 1
-
-
-
+{-# OPTIONS_GHC -Wno-missing-signatures #-}
+
+module Main (main) where
+
+import Data.Graph.Dom as G
+import Data.Tree
+import System.Exit
+
+import Test.HUnit hiding (Node,Path)
+-- import Test.Framework.Providers.QuickCheck2
+-- import Test.QuickCheck (Property, (===))
+-- import Test.QuickCheck.Function (Fun, apply)
+-- import Test.QuickCheck.Poly (A, OrdA, B, OrdB, C)
+
+-- main = defaultMain
+--   [ test_dom
+--   , testtest_pdom
+--   , test_idom
+--   , test_ipdom
+--   , test_domTree
+--   , test_pdomTree
+--   ]
+
+g0 :: Graph
+g0 = fromAdj
+  [(1,[2,3])
+  ,(2,[3])
+  ,(3,[4])
+  ,(4,[3,5,6])
+  ,(5,[7])
+  ,(6,[7])
+  ,(7,[4,8])
+  ,(8,[3,9,10])
+  ,(9,[1])
+  ,(10,[7])]
+
+g1 :: Graph
+g1 = fromAdj
+  [(0,[1])
+  ,(1,[2,3])
+  ,(2,[7])
+  ,(3,[4])
+  ,(4,[5,6])
+  ,(5,[7])
+  ,(6,[4])
+  ,(7,[])]
+
+main = do
+  counts <- runTestTT tests
+  putStrLn $ showCounts counts
+  if (errors counts + failures counts) > 0
+    then exitWith $ ExitFailure 1
+    else exitWith   ExitSuccess
+
+tests = TestList $ map TestCase [dom0, dom1, pdom0, pdom1, ipdom0, ipdom1, dom_t_g0, dom_t_g1, dom_pt_g0, dom_pt_g1]
+
+g0_rooted, g1_rooted :: Rooted
+g0_rooted = (1,g0)
+g1_rooted = (0,g1)
+
+dom0 = assertEqual "dom g0"
+        [(2,[1]),(3,[1]),(4,[3,1]),(5,[4,3,1]),(6,[4,3,1]),(7,[4,3,1]),(8,[7,4,3,1]),(9,[8,7,4,3,1]),(10,[8,7,4,3,1])]
+        (dom g0_rooted)
+
+dom1 = assertEqual "dom g1"
+        [(1,[0]),(2,[1,0]),(3,[1,0]),(7,[1,0]),(4,[3,1,0]),(5,[4,3,1,0]),(6,[4,3,1,0])]
+        (dom g1_rooted)
+
+pdom0 = assertEqual "pdom g0"
+        [(9,[1]),(8,[9,1]),(7,[8,9,1]),(4,[7,8,9,1]),(5,[7,8,9,1]),(6,[7,8,9,1]),(10,[7,8,9,1]),(3,[4,7,8,9,1]),(2,[3,4,7,8,9,1])]
+        (pdom g0_rooted)
+
+pdom1 = assertEqual "pdom g1"
+        []
+        (pdom g1_rooted)
+
+ipdom0 = assertEqual "ipdom g0"
+          [(10,7),(8,9),(9,1),(7,8),(6,7),(5,7),(4,7),(3,4),(2,3),(1,1)]
+          (ipdom g0_rooted)
+
+ipdom1 = assertEqual "ipdom g1"
+          [(0,0)]
+          (ipdom g1_rooted)
+
+dom_t_g0 = assertEqual "domTree g0"
+            (  Node {rootLabel = 1, subForest = [Node {rootLabel = 2, subForest = []},Node {rootLabel = 3, subForest = [Node {rootLabel = 4, subForest = [Node {rootLabel = 5, subForest = []},Node {rootLabel = 6, subForest = []},Node {rootLabel = 7, subForest = [Node {rootLabel = 8, subForest = [Node {rootLabel = 9, subForest = []},Node {rootLabel = 10, subForest = []}]}]}]}]}]}  )
+            (domTree g0_rooted)
+
+dom_t_g1 = assertEqual "domTree g1"
+            (  Node {rootLabel = 0, subForest = [Node {rootLabel = 1, subForest = [Node {rootLabel = 2, subForest = []},Node {rootLabel = 3, subForest = [Node {rootLabel = 4, subForest = [Node {rootLabel = 5, subForest = []},Node {rootLabel = 6, subForest = []}]}]}, Node {rootLabel = 7, subForest = []}]}]}  )
+            (domTree g1_rooted)
+
+dom_pt_g0 = assertEqual "pdomTree g0"
+              (  Node {rootLabel = 1, subForest = [Node {rootLabel = 9, subForest = [Node {rootLabel = 8, subForest = [Node {rootLabel = 7, subForest = [Node {rootLabel = 4, subForest = [Node {rootLabel = 3, subForest = [Node {rootLabel = 2, subForest = []}]}]},Node {rootLabel = 5, subForest = []},Node {rootLabel = 6, subForest = []},Node {rootLabel = 10, subForest = []}]}]}]}]}  )
+              (pdomTree g0_rooted)
+
+dom_pt_g1 = assertEqual "pdomTree g1"
+              (  Node {rootLabel = 0, subForest = []}  )
+              (pdomTree g1_rooted)
+
+
+
+
+-- applyDomFunctions :: Rooted
+--                   -> ([(Node, Path)], [(Node, Path)], [(Node, Node)], [(Node, Node)], Tree Node, Tree Node)
+-- applyDomFunctions g = (dom g, pdom g, idom g, ipdom g, domTree g, pdomTree g)
+
+-- g0_expected :: ([(Node, Path)], [(Node, Path)], [(Node, Node)], [(Node, Node)], Tree Node, Tree Node)
+-- g0_expected = (
+--   [(2,[1]),(3,[1]),(4,[3,1]),(5,[4,3,1]),(6,[4,3,1]),(7,[4,3,1]),(8,[7,4,3,1]),(9,[8,7,4,3,1]),(10,[8,7,4,3,1])],
+--   [(9,[1]),(8,[9,1]),(7,[8,9,1]),(4,[7,8,9,1]),(5,[7,8,9,1]),(6,[7,8,9,1]),(10,[7,8,9,1]),(3,[4,7,8,9,1]),(2,[3,4,7,8,9,1])],
+--   [(10,8),(7,4),(9,8),(1,1),(8,7),(3,1),(4,3),(6,4),(5,4),(2,1)],
+--   [(10,7),(8,9),(9,1),(7,8),(6,7),(5,7),(4,7),(3,4),(2,3),(1,1)],
+  -- Node {rootLabel = 1, subForest = [Node {rootLabel = 2, subForest = []},Node {rootLabel = 3, subForest = [Node {rootLabel = 4, subForest = [Node {rootLabel = 5, subForest = []},Node {rootLabel = 6, subForest = []},Node {rootLabel = 7, subForest = [Node {rootLabel = 8, subForest = [Node {rootLabel = 9, subForest = []},Node {rootLabel = 10, subForest = []}]}]}]}]}]},
+  -- Node {rootLabel = 1, subForest = [Node {rootLabel = 9, subForest = [Node {rootLabel = 8, subForest = [Node {rootLabel = 7, subForest = [Node {rootLabel = 4, subForest = [Node {rootLabel = 3, subForest = [Node {rootLabel = 2, subForest = []}]}]},Node {rootLabel = 5, subForest = []},Node {rootLabel = 6, subForest = []},Node {rootLabel = 10, subForest = []}]}]}]}]}
+--   )
+
+-- g1_expected :: ([(Node, Path)], [(Node, Path)], [(Node, Node)], [(Node, Node)], Tree Node, Tree Node)
+-- g1_expected = (
+    -- [(1,[0]),(2,[1,0]),(3,[1,0]),(7,[1,0]),(4,[3,1,0]),(5,[4,3,1,0]),(6,[4,3,1,0])],
+    -- [],
+    -- [(7,1),(6,4),(4,3),(5,4),(3,1),(2,1),(1,0),(0,0)],[(0,0)],
+    -- Node {rootLabel = 0, subForest = [Node {rootLabel = 1, subForest = [Node {rootLabel = 2, subForest = []},Node {rootLabel = 3, subForest = [Node {rootLabel = 4, subForest = [Node {rootLabel = 5, subForest = []},Node {rootLabel = 6, subForest = []}]}]},
+    -- Node {rootLabel = 7, subForest = []}]}]},Node {rootLabel = 0, subForest = []})
+
+-- main :: IO ()
+-- main = do
+--     let g0_result = applyDomFunctions (1,g0)
+--     let g1_result = applyDomFunctions (0,g1)
+--     if g0_result == g0_expected && g1_result == g1_expected
+--         then exitWith ExitSuccess
+--         else exitWith $ ExitFailure 1
+
+
+