diff --git a/src/Constrained/Core.hs b/src/Constrained/Core.hs
index 034e174..e4f8497 100644
--- a/src/Constrained/Core.hs
+++ b/src/Constrained/Core.hs
@@ -129,4 +129,3 @@ instance Typeable c => Show (Evidence c) where
 -- | Take the union of two `Maybe` values with a given union operator
 unionWithMaybe :: (a -> a -> a) -> Maybe a -> Maybe a -> Maybe a
 unionWithMaybe f ma ma' = (f <$> ma <*> ma') <|> ma <|> ma'
-
diff --git a/src/Constrained/NumOrd.hs b/src/Constrained/NumOrd.hs
index 7ae77ea..8314392 100644
--- a/src/Constrained/NumOrd.hs
+++ b/src/Constrained/NumOrd.hs
@@ -64,6 +64,7 @@ import Constrained.List
 import Constrained.PrettyUtils
 import Control.Applicative ((<|>))
 import Control.Arrow (first)
+import Data.Containers.ListUtils
 import Data.Foldable
 import Data.Kind
 import Data.List (nub)
@@ -362,17 +363,6 @@ conformsToNumSpec i (NumSpecInterval ml mu) = maybe True (<= i) ml && maybe True
 -- implementations are found here
 -- =====================================================================
 
--- | Strip out duplicates (in n-log(n) time, by building an intermediate Set)
-nubOrd :: Ord a => [a] -> [a]
-nubOrd =
-  loop mempty
-  where
-    loop _ [] = []
-    loop s (a : as)
-      | a `Set.member` s = loop s as
-      | otherwise =
-          let s' = Set.insert a s in s' `seq` a : loop s' as
-
 -- | Builds a MemberSpec, but returns an Error spec if the list is empty
 nubOrdMemberSpec :: Ord a => String -> [a] -> Specification a
 nubOrdMemberSpec message xs =
@@ -936,7 +926,7 @@ instance Logic IntW where
 
   propagateMemberSpec AddW (HOLE :<: i) es =
     memberSpec
-      (nub $ mapMaybe (safeSubtract i) (NE.toList es))
+      (nubOrd $ mapMaybe (safeSubtract i) (NE.toList es))
       ( NE.fromList
           [ "propagateSpecFn on (" ++ show i ++ " +. HOLE)"
           , "The Spec is a MemberSpec = " ++ show es -- show (MemberSpec @HasSpec @TS es)