diff --git a/transformations/ArrayUsageCheck.hs b/transformations/ArrayUsageCheck.hs
index 6225ad4..2be7e89 100644
--- a/transformations/ArrayUsageCheck.hs
+++ b/transformations/ArrayUsageCheck.hs
@@ -142,6 +142,8 @@ data FlattenedExp
   | Modulo (Set.Set FlattenedExp) (Set.Set FlattenedExp)
   | Divide (Set.Set FlattenedExp) (Set.Set FlattenedExp)
 
+--TODO change the A.Variable to Var, and automatically derive Eq and Ord
+
 instance Eq FlattenedExp where
   a == b = EQ == compare a b
 
@@ -159,10 +161,6 @@ instance Ord FlattenedExp where
   compare (Divide ltop lbottom) (Divide rtop rbottom)
     = combineCompare [compare ltop rtop, compare lbottom rbottom]
 
-customVarCompare :: A.Variable -> A.Variable -> Ordering
-customVarCompare (A.Variable _ (A.Name _ _ lname)) (A.Variable _ (A.Name _ _ rname)) = compare lname rname
--- TODO the rest
-
 onlyConst :: [FlattenedExp] -> Maybe Integer
 onlyConst [] = Just 0
 onlyConst ((Const n):es) = liftM2 (+) (return n) $ onlyConst es
diff --git a/transformations/UsageCheck.hs b/transformations/UsageCheck.hs
index c60098c..aca5a3d 100644
--- a/transformations/UsageCheck.hs
+++ b/transformations/UsageCheck.hs
@@ -29,6 +29,16 @@ import Metadata
 
 newtype Var = Var A.Variable
 
+customVarCompare :: A.Variable -> A.Variable -> Ordering
+customVarCompare (A.Variable _ (A.Name _ _ lname)) (A.Variable _ (A.Name _ _ rname)) = compare lname rname
+-- TODO the rest
+
+instance Eq Var where
+  a == b = EQ == compare a b
+
+instance Ord Var where
+  compare (Var a) (Var b) = customVarCompare a b
+
 data Vars = Vars {
   readVars :: Set.Set Var
   ,writtenVars :: Set.Set Var