diff --git a/CHANGES b/CHANGES
--- a/CHANGES
+++ b/CHANGES
@@ -1,3 +1,7 @@
+Changes in 1.3.3.1
+  * Remove mtl dependency (removed unnecessary imports which were incompatible with mtl 2.3)
+  * Fix implementation of little-endian PatriciaTrees
+
 Changes in 1.3.3
   * Updates to handle MonadFail changes in GHC 8.x
   * Updates to fix compile issues in GHC 9
diff --git a/EdisonCore.cabal b/EdisonCore.cabal
--- a/EdisonCore.cabal
+++ b/EdisonCore.cabal
@@ -1,7 +1,7 @@
 Name:           EdisonCore
 Cabal-Version:  >= 1.10
 Build-Type:     Simple
-Version:        1.3.3
+Version:        1.3.3.1
 License:        MIT
 License-File:   COPYRIGHT
 Author:         Chris Okasaki
@@ -55,7 +55,6 @@
      Data.Edison.Seq.SizedSeq
   Build-Depends:
      base == 4.*,
-     mtl,
      QuickCheck >= 2.8.2 && < 3,
      EdisonAPI >= 1.3.3 && < 1.4,
      containers,
diff --git a/src/Data/Edison/Assoc/PatriciaLoMap.hs b/src/Data/Edison/Assoc/PatriciaLoMap.hs
--- a/src/Data/Edison/Assoc/PatriciaLoMap.hs
+++ b/src/Data/Edison/Assoc/PatriciaLoMap.hs
@@ -121,7 +121,7 @@
 rmakeB _ _ t E = t
 rmakeB p m t0 t1 = B p m t0 t1
 
-lowestBit :: Int32 -> Int32
+lowestBit :: Word -> Word
 lowestBit x = x .&. (-x)
 
 branchingBit :: Int -> Int -> Int
@@ -129,10 +129,13 @@
   fromIntegral (lowestBit (fromIntegral p0 `xor` fromIntegral p1))
 
 mask :: Int -> Int -> Int
-mask p m = fromIntegral (fromIntegral p .&. (fromIntegral m - (1 :: Int32)))
+mask p m = fromIntegral (fromIntegral p .&. (fromIntegral m - (1 :: Word)))
 
+shorter :: Int -> Int -> Bool
+shorter m n = fromIntegral m < (fromIntegral n :: Word)
+
 zeroBit :: Int -> Int -> Bool
-zeroBit p m = (fromIntegral p) .&. (fromIntegral m) == (0 :: Int32)
+zeroBit p m = (fromIntegral p) .&. (fromIntegral m) == (0 :: Word)
 
 matchPrefix :: Int -> Int -> Int -> Bool
 matchPrefix k p m = mask k m == p
@@ -168,11 +171,11 @@
 
 union :: FM a -> FM a -> FM a
 union s@(B p m s0 s1) t@(B q n t0 t1)
-  | m < n    = if matchPrefix q p m then
+  | shorter m n = if matchPrefix q p m then
                   if zeroBit q m then B p m (union s0 t) s1
                                  else B p m s0 (union s1 t)
                 else join p s q t
-  | m > n    = if matchPrefix p q n then
+  | shorter n m = if matchPrefix p q n then
                   if zeroBit p n then B q n (union s t0) t1
                                  else B q n t0 (union s t1)
                 else join p s q t
@@ -320,11 +323,11 @@
 
 unionl :: FM a -> FM a -> FM a
 unionl s@(B p m s0 s1) t@(B q n t0 t1)
-  | m < n    = if matchPrefix q p m then
+  | shorter m n = if matchPrefix q p m then
                   if zeroBit q m then B p m (unionl s0 t) s1
                                  else B p m s0 (unionl s1 t)
                 else join p s q t
-  | m > n    = if matchPrefix p q n then
+  | shorter n m = if matchPrefix p q n then
                   if zeroBit p n then B q n (unionl s t0) t1
                                  else B q n t0 (unionl s t1)
                 else join p s q t
@@ -341,11 +344,11 @@
 
 unionr :: FM a -> FM a -> FM a
 unionr s@(B p m s0 s1) t@(B q n t0 t1)
-  | m < n    = if matchPrefix q p m then
+  | shorter m n = if matchPrefix q p m then
                   if zeroBit q m then B p m (unionr s0 t) s1
                                  else B p m s0 (unionr s1 t)
                 else join p s q t
-  | m > n    = if matchPrefix p q n then
+  | shorter n m = if matchPrefix p q n then
                   if zeroBit p n then B q n (unionr s t0) t1
                                  else B q n t0 (unionr s t1)
                 else join p s q t
@@ -362,11 +365,11 @@
 
 unionWith :: (a -> a -> a) -> FM a -> FM a -> FM a
 unionWith f s@(B p m s0 s1) t@(B q n t0 t1)
-  | m < n    = if matchPrefix q p m then
+  | shorter m n = if matchPrefix q p m then
                   if zeroBit q m then B p m (unionWith f s0 t) s1
                                  else B p m s0 (unionWith f s1 t)
                 else join p s q t
-  | m > n    = if matchPrefix p q n then
+  | shorter n m = if matchPrefix p q n then
                   if zeroBit p n then B q n (unionWith f s t0) t1
                                  else B q n t0 (unionWith f s t1)
                 else join p s q t
@@ -383,11 +386,11 @@
 
 intersectionWith :: (a -> b -> c) -> FM a -> FM b -> FM c
 intersectionWith f s@(B p m s0 s1) t@(B q n t0 t1)
-  | m < n    = if matchPrefix q p m then
+  | shorter m n = if matchPrefix q p m then
                   if zeroBit q m then intersectionWith f s0 t
                                  else intersectionWith f s1 t
                 else E
-  | m > n    = if matchPrefix p q n then
+  | shorter n m = if matchPrefix p q n then
                   if zeroBit p n then intersectionWith f s t0
                                  else intersectionWith f s t1
                 else E
@@ -406,11 +409,11 @@
 
 difference :: FM a -> FM b -> FM a
 difference s@(B p m s0 s1) t@(B q n t0 t1)
-  | m < n    = if matchPrefix q p m then
+  | shorter m n = if matchPrefix q p m then
                   if zeroBit q m then lmakeB p m (difference s0 t) s1
                                  else rmakeB p m s0 (difference s1 t)
                 else s
-  | m > n    = if matchPrefix p q n then
+  | shorter n m = if matchPrefix p q n then
                   if zeroBit p n then difference s t0
                                  else difference s t1
                 else s
@@ -430,10 +433,10 @@
 
 subset' :: FM t -> FM t1 -> Ordering
 subset' s@(B p m s0 s1) (B q n t0 t1)
-  | m < n    = GT
-  | m > n    = if matchPrefix p q n then
-                  if zeroBit p n then subset' s t0
-                                 else subset' s t1
+  | shorter m n = GT
+  | shorter n m = if matchPrefix p q n then
+                  if zeroBit p n then subset' s t0 SG.<> LT
+                                 else subset' s t1 SG.<> LT
                 else GT
   | otherwise = if p == q then case (subset' s0 t0,subset' s1 t1) of
                                   (GT,_)  -> GT
@@ -449,8 +452,8 @@
 
 subset :: FM a -> FM b -> Bool
 subset s@(B p m s0 s1) (B q n t0 t1)
-  | m < n    = False
-  | m > n    = matchPrefix p q n && (if zeroBit p n then subset s t0
+  | shorter m n = False
+  | shorter n m = matchPrefix p q n && (if zeroBit p n then subset s t0
                                                      else subset s t1)
   | otherwise = (p == q) && subset s0 t0 && subset s1 t1
 subset (B _ _ _ _) _ = False
@@ -507,11 +510,11 @@
 
 unionWithKey :: (Int -> a -> a -> a) -> FM a -> FM a -> FM a
 unionWithKey f s@(B p m s0 s1) t@(B q n t0 t1)
-  | m < n    = if matchPrefix q p m then
+  | shorter m n = if matchPrefix q p m then
                   if zeroBit q m then B p m (unionWithKey f s0 t) s1
                                  else B p m s0 (unionWithKey f s1 t)
                 else join p s q t
-  | m > n    = if matchPrefix p q n then
+  | shorter n m = if matchPrefix p q n then
                   if zeroBit p n then B q n (unionWithKey f s t0) t1
                                  else B q n t0 (unionWithKey f s t1)
                 else join p s q t
@@ -528,11 +531,11 @@
 
 intersectionWithKey :: (Int -> a -> b -> c) -> FM a -> FM b -> FM c
 intersectionWithKey f s@(B p m s0 s1) t@(B q n t0 t1)
-  | m < n    = if matchPrefix q p m then
+  | shorter m n = if matchPrefix q p m then
                   if zeroBit q m then intersectionWithKey f s0 t
                                  else intersectionWithKey f s1 t
                 else E
-  | m > n    = if matchPrefix p q n then
+  | shorter n m = if matchPrefix p q n then
                   if zeroBit p n then intersectionWithKey f s t0
                                  else intersectionWithKey f s t1
                 else E
diff --git a/src/Data/Edison/Assoc/TernaryTrie.hs b/src/Data/Edison/Assoc/TernaryTrie.hs
--- a/src/Data/Edison/Assoc/TernaryTrie.hs
+++ b/src/Data/Edison/Assoc/TernaryTrie.hs
@@ -59,7 +59,7 @@
 import qualified Data.Edison.Seq as S
 import qualified Data.List as L
 import qualified Control.Monad.Fail as Fail
-import Control.Monad.Identity
+import Control.Monad
 import Data.Monoid
 import Data.Semigroup as SG
 import Data.Maybe (isNothing)
@@ -637,7 +637,7 @@
       = foldFMB r . foldFMB m . foldMV v . foldFMB l
 
 
--- FIXME, undestand this code to strictify it
+-- FIXME, understand this code to strictify it
 foldr' = foldr
 foldl' :: (a -> b -> a) -> a -> FM t b -> a
 foldl' = foldl
@@ -700,7 +700,7 @@
 
 
 
--- FIXME, undestand this code to strictify it
+-- FIXME, understand this code to strictify it
 foldr1' = foldr1
 foldl1' :: (b -> b -> b) -> FM k b -> b
 foldl1' = foldl1
diff --git a/src/Data/Edison/Coll/EnumSet.hs b/src/Data/Edison/Coll/EnumSet.hs
--- a/src/Data/Edison/Coll/EnumSet.hs
+++ b/src/Data/Edison/Coll/EnumSet.hs
@@ -33,7 +33,7 @@
 -- > forall x y::A, x < y <==> toEnum x < toEnum y
 --
 -- Derived @Eq@, @Ord@ and @Enum@ instances will fulfill these conditions, if
--- the enumerated type has sufficently few constructors.
+-- the enumerated type has sufficiently few constructors.
 
 {-
 Copyright (c) 2006, 2008, David F. Place
@@ -151,7 +151,7 @@
             , toBits
             , fromBits
 
-            -- * Documenation
+            -- * Documentation
             , moduleName
 )  where
 
@@ -479,7 +479,7 @@
 unsafeMapMonotonic = map
 
 -- | /O(1)/ Changes the type of the elements in the set without changing
---   the representation.  Equivalant to @map (toEnum . fromEnum)@, and
+--   the representation.  Equivalent to @map (toEnum . fromEnum)@, and
 --   to @(fromBits . toBits)@.  This method is operationally a no-op.
 setCoerce :: (Enum a, Enum b) => Set a -> Set b
 setCoerce (Set w) = Set w
@@ -553,16 +553,16 @@
 
 foldl1 :: (Ord a, Enum a) => (a -> a -> a) -> Set a -> a
 foldl1 _ (Set 0) = error (moduleName++".foldl1: empty set")
-foldl1 f (Set w) = foldlBits folder (toEnum mininum) (clearBit w mininum)
+foldl1 f (Set w) = foldlBits folder (toEnum minimum) (clearBit w minimum)
   where
-    mininum = lsb w
+    minimum = lsb w
     folder z i = f z (toEnum i)
 
 foldl1' :: (Ord a, Enum a) => (a -> a -> a) -> Set a -> a
 foldl1' _ (Set 0) = error (moduleName++".foldl1': empty set")
-foldl1' f (Set w) = foldlBits' folder (toEnum mininum) (clearBit w mininum)
+foldl1' f (Set w) = foldlBits' folder (toEnum minimum) (clearBit w minimum)
   where
-    mininum = lsb w
+    minimum = lsb w
     folder z i = f z (toEnum i)
 
 {--------------------------------------------------------------------
diff --git a/src/Data/Edison/Seq/BankersQueue.hs b/src/Data/Edison/Seq/BankersQueue.hs
--- a/src/Data/Edison/Seq/BankersQueue.hs
+++ b/src/Data/Edison/Seq/BankersQueue.hs
@@ -58,7 +58,7 @@
 import Data.Monoid
 import Data.Semigroup as SG
 import qualified Control.Monad.Fail as Fail
-import Control.Monad.Identity
+import Control.Monad
 import Test.QuickCheck
 
 -- signatures for exported functions
diff --git a/src/Data/Edison/Seq/BraunSeq.hs b/src/Data/Edison/Seq/BraunSeq.hs
--- a/src/Data/Edison/Seq/BraunSeq.hs
+++ b/src/Data/Edison/Seq/BraunSeq.hs
@@ -73,7 +73,7 @@
 
 import qualified Control.Applicative as App
 import qualified Control.Monad.Fail as Fail
-import Control.Monad.Identity
+import Control.Monad
 import Data.Maybe
 import Data.Monoid
 import Data.Semigroup as SG
diff --git a/src/Data/Edison/Seq/Defaults.hs b/src/Data/Edison/Seq/Defaults.hs
--- a/src/Data/Edison/Seq/Defaults.hs
+++ b/src/Data/Edison/Seq/Defaults.hs
@@ -18,7 +18,7 @@
                        zip,zip3,zipWith,zipWith3,unzip,unzip3,null)
 
 import qualified Control.Monad.Fail as Fail
-import Control.Monad.Identity
+import Control.Monad
 import Data.Char (isSpace)
 
 import Data.Edison.Prelude ( runFail_ )
diff --git a/src/Data/Edison/Seq/FingerSeq.hs b/src/Data/Edison/Seq/FingerSeq.hs
--- a/src/Data/Edison/Seq/FingerSeq.hs
+++ b/src/Data/Edison/Seq/FingerSeq.hs
@@ -41,7 +41,7 @@
 import qualified Data.Edison.Seq as S
 import Data.Edison.Seq.Defaults
 import qualified Control.Monad.Fail as Fail
-import Control.Monad.Identity
+import Control.Monad
 import Data.Monoid
 import Data.Semigroup as SG
 import Test.QuickCheck
diff --git a/src/Data/Edison/Seq/MyersStack.hs b/src/Data/Edison/Seq/MyersStack.hs
--- a/src/Data/Edison/Seq/MyersStack.hs
+++ b/src/Data/Edison/Seq/MyersStack.hs
@@ -53,7 +53,7 @@
 import qualified Data.Edison.Seq as S ( Sequence(..) )
 import Data.Edison.Seq.Defaults
 import qualified Control.Monad.Fail as Fail
-import Control.Monad.Identity
+import Control.Monad
 import Data.Monoid
 import Data.Semigroup as SG
 import Test.QuickCheck
diff --git a/src/Data/Edison/Seq/RandList.hs b/src/Data/Edison/Seq/RandList.hs
--- a/src/Data/Edison/Seq/RandList.hs
+++ b/src/Data/Edison/Seq/RandList.hs
@@ -59,7 +59,7 @@
 import qualified Data.Edison.Seq as S( Sequence(..) )
 import Data.Edison.Seq.Defaults
 import qualified Control.Monad.Fail as Fail
-import Control.Monad.Identity
+import Control.Monad
 import Data.Monoid
 import Data.Semigroup as SG
 import Test.QuickCheck