diff --git a/3/3.hs b/3/3.hs
index 7429be9..312593e 100644
--- a/3/3.hs
+++ b/3/3.hs
@@ -72,6 +72,10 @@ data IntervalTree a b = Node { itLeft :: IntervalTree a b
                              }
                       | Empty a a deriving (Show, Eq)
 
+rightOf, leftOf :: Ord a => Interval a -> a -> Bool
+rightOf (Interval (start, _)) x = x < start
+leftOf (Interval (_, end)) x = end <= x
+
 insert :: (Ord a, Bits a, Num a) => (Interval a, b) -> IntervalTree a b -> IntervalTree a b
 insert o@(interval, _) tree = case tree of
   Empty start end -> go start end (start + half (end - start))
@@ -84,8 +88,6 @@ insert o@(interval, _) tree = case tree of
       | interval `rightOf` center  = Node (Empty start center) center [] (insert o (Empty center end))
       | otherwise                  = Node (Empty start center) center [o] (Empty center end)
 
-    rightOf (Interval (start, _)) x = x < start
-    leftOf (Interval (_, end)) x = end <= x
     half = flip shift (-1)
 
 includingIntervals :: Ord a => Interval a -> IntervalTree a b -> [(Interval a, b)]
@@ -93,7 +95,11 @@ includingIntervals interval = go []
   where
     go acc t = case t of
       Empty _ _ -> acc
-      Node l _ is r -> go (go (filter (\(i,_) -> i `includes` interval) is ++ acc) l) r
+      Node l center is r | interval `leftOf` center  -> go (acc' is acc) l
+      Node l center is r | interval `rightOf` center -> go (acc' is acc) r
+      Node l center is r                             -> go (go (acc' is acc) l) r
+      where
+        acc' is acc = filter (\(i,_) -> i `includes` interval) is ++ acc
 
     includes (Interval (start1, end1)) (Interval (start2, end2))
       = start1 <= start2 && end2 <= end1
@@ -121,8 +127,8 @@ intervalTreeSolve rects =
       (xTree, yTree) = rectIntervalTrees rects
       overlapArea = length . filter (\c -> isOverlapCell (cellRects xTree yTree c) c) $ cells
   in overlapArea
-  where      
-    cellRects xTree yTree (x,y) = 
+  where
+    cellRects xTree yTree (x,y) =
       nub . map snd
       $ includingIntervals (Interval (x, x+1)) xTree ++ includingIntervals (Interval (y, y+1)) yTree