diff --git a/hcdt.cabal b/hcdt.cabal
index 2f61626..534a294 100644
--- a/hcdt.cabal
+++ b/hcdt.cabal
@@ -30,6 +30,8 @@ library
   build-depends:       base >= 4.7 && < 5
                      , containers >= 0.6.4.1
                      , indexed-traversable >= 0.1.2
+                     , hashable >= 1.4.0.0
+                     , witherable >= 0.4
   if impl(ghc >= 9.4)
     build-depends:     system-cxx-std-lib == 1.0
   elif os(darwin) || os(freebsd)
diff --git a/src/Geometry/HCDT/Types.hs b/src/Geometry/HCDT/Types.hs
index d60beea..4491073 100644
--- a/src/Geometry/HCDT/Types.hs
+++ b/src/Geometry/HCDT/Types.hs
@@ -1,6 +1,8 @@
 {-# LANGUAGE InstanceSigs #-}
+
 module Geometry.HCDT.Types
   where
+import           Data.Hashable      (Hashable, hashWithSalt)
 import           Data.IntMap.Strict (IntMap)
 import           Data.List          (sort)
 
@@ -15,6 +17,8 @@ data Edge = Edge Int Int
 instance Eq Edge where
     (==) :: Edge -> Edge -> Bool
     Edge i j == Edge i' j' = (i == i' && j == j') || (i == j' && j == i')
+instance Hashable Edge where
+  hashWithSalt s (Edge m1 m2) = hashWithSalt s (min m1 m2) `hashWithSalt` (max m1 m2)
 
 data Vertex = Vertex Double Double
   deriving (Show, Eq)
diff --git a/src/Geometry/HCDT/Utils.hs b/src/Geometry/HCDT/Utils.hs
index 8bf0d82..9110b2e 100644
--- a/src/Geometry/HCDT/Utils.hs
+++ b/src/Geometry/HCDT/Utils.hs
@@ -8,9 +8,9 @@ import Geometry.HCDT.Types
     ( Triangulation(_triangles), Edge(..), Triangle(..) ) 
 import           Data.Sequence as DS     (Seq, fromList, (><), filter, deleteAt) 
 import           Data.Maybe              (isNothing, fromJust)
-import           Data.Foldable           (find, toList)
+import           Data.Foldable           (find)
 import           Data.Foldable.WithIndex (ifind)
-import           Data.List               (nub)
+import           Witherable              (hashNub)
 
 triangleEdges :: Triangle -> Seq Edge
 triangleEdges (Triangle i j k) = fromList [Edge i j, Edge j k, Edge i k]
@@ -46,4 +46,4 @@ partitionEdges triangulation = (exEdges, inEdges)
   where
     edges = allEdges triangulation
     exEdges = DS.filter (isUnique edges) edges
-    inEdges = DS.fromList $ nub $ toList $ DS.filter (not . isUnique edges) edges
\ No newline at end of file
+    inEdges = hashNub $ DS.filter (not . isUnique edges) edges
\ No newline at end of file