diff --git a/src/Data/Xournal/BBox.hs b/src/Data/Xournal/BBox.hs
--- a/src/Data/Xournal/BBox.hs
+++ b/src/Data/Xournal/BBox.hs
@@ -1,4 +1,4 @@
-{-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE TypeFamilies, StandaloneDeriving #-}
 
 -----------------------------------------------------------------------------
 -- |
@@ -10,16 +10,20 @@
 -- Stability   : experimental
 -- Portability : GHC
 --
+-----------------------------------------------------------------------------
 
 module Data.Xournal.BBox where
 
 import Control.Monad
 import Data.ByteString hiding (map,maximum,minimum)
+-- import qualified Data.Sequence as Seq
 import Data.Xournal.Generic
 import Data.Xournal.Simple
 import Data.Strict.Tuple 
+import qualified Data.Foldable as F
 import Data.Monoid
 import Prelude hiding (fst,snd)
+import qualified Prelude as Prelude (fst,snd)
 
 data BBox = BBox { bbox_upperleft :: (Double,Double) 
                  , bbox_lowerright :: (Double,Double) } 
@@ -48,13 +52,38 @@
              in  BBox { bbox_upperleft = (minimum xs, minimum ys)
                       , bbox_lowerright = (maximum xs, maximum ys) } 
 
+mkbboxF :: (F.Foldable m, Functor m) => m (Double,Double) -> BBox 
+mkbboxF lst = 
+  let xs = fmap Prelude.fst lst  
+      ys = fmap Prelude.snd lst 
+  in BBox{bbox_upperleft=(F.minimum xs, F.minimum ys)
+         ,bbox_lowerright=(F.maximum xs, F.maximum ys)}
+
 dimToBBox :: Dimension -> BBox 
 dimToBBox (Dim w h) = BBox (0,0) (w,h)
 
+-- | transform BBox
+         
+xformBBox :: ((Double,Double) -> (Double,Double)) -> BBox -> BBox 
+xformBBox f (BBox c1 c2) = BBox (f c1) (f c2)
+
+-- | 
+
+moveBBoxToOrigin :: BBox -> BBox 
+moveBBoxToOrigin (BBox (x0,y0) (x1,y1)) = BBox (0,0) (x1-x0,y1-y0)
+
+-- |
+
+moveBBoxByOffset :: (Double,Double) -> BBox -> BBox 
+moveBBoxByOffset (xoff,yoff) (BBox (x0,y0) (x1,y1)) = BBox (x0+xoff,y0+yoff) (x1+xoff,y1+yoff)
+
+moveBBoxULCornerTo :: (Double,Double) -> BBox -> BBox 
+moveBBoxULCornerTo (x,y) b@(BBox (x0,y0) _) = moveBBoxByOffset (x-x0,y-y0) b 
+
 intersectBBox :: BBox -> BBox -> Maybe BBox
 intersectBBox (BBox (x1,y1) (x2,y2)) (BBox (x3,y3) (x4,y4)) = do 
   guard $ (x1 <= x3 && x3 <= x2) || (x3 <= x1 && x1 <= x4 ) 
-  guard $ (y1 <= y3 && y3 <= y4) || (y3 <= y1 && y1 <= y4 )
+  guard $ (y1 <= y3 && y3 <= y2) || (y3 <= y1 && y1 <= y4 )
   let x5 = if x1 <= x3 then x3 else x1 
       y5 = if y1 <= y3 then y3 else y1 
       x6 = min x2 x4 
@@ -79,16 +108,23 @@
      
 data ULMaybe a = Bottom | Middle a | Top      
      
+deriving instance Show a => Show (ULMaybe a)
+
+deriving instance Eq a => Eq (ULMaybe a)
+                                     
 newtype IntersectBBox = Intersect { unIntersect :: ULMaybe BBox } 
+                        deriving (Show,Eq)
 
 newtype UnionBBox = Union { unUnion :: ULMaybe BBox }
+                    deriving (Show,Eq)
      
 instance Monoid (IntersectBBox) where 
   (Intersect Bottom) `mappend` _ = Intersect Bottom
   _ `mappend` (Intersect Bottom) = Intersect Bottom 
   (Intersect Top) `mappend` x = x 
   x `mappend` (Intersect Top) = x 
-  (Intersect (Middle x)) `mappend` (Intersect (Middle y)) = fromMaybe (x `intersectBBox` y)
+  (Intersect (Middle x)) `mappend` (Intersect (Middle y)) = 
+    maybe (Intersect Bottom) (Intersect . Middle) (x `intersectBBox` y)
   mempty = Intersect Top 
   
 instance Monoid (UnionBBox) where
@@ -106,7 +142,7 @@
   
 instance Maybeable IntersectBBox where
   type ElemType IntersectBBox = BBox
-  toMaybe (Intersect Bottom) = error "empty intersectbbox"
+  toMaybe (Intersect Bottom) = Nothing  -- error "empty intersectbbox"
   toMaybe (Intersect Top) = Nothing 
   toMaybe (Intersect (Middle x)) = Just x 
   fromMaybe Nothing = Intersect Top 
@@ -114,7 +150,7 @@
   
 instance Maybeable UnionBBox where
   type ElemType UnionBBox = BBox
-  toMaybe (Union Bottom) = error "empty unionbbox"
+  toMaybe (Union Bottom) = Nothing -- error "empty unionbbox"
   toMaybe (Union Top) = Nothing 
   toMaybe (Union (Middle x)) = Just x 
   fromMaybe Nothing = Union Top 
diff --git a/src/Data/Xournal/Buffer.hs b/src/Data/Xournal/Buffer.hs
--- a/src/Data/Xournal/Buffer.hs
+++ b/src/Data/Xournal/Buffer.hs
@@ -15,10 +15,10 @@
 
 import Data.IntMap 
 import Data.Xournal.Select
-import Data.Xournal.Simple
+-- import Data.Xournal.Simple
 import Data.Xournal.Generic
 import Data.Xournal.BBox
-import Data.Xournal.Map
+-- import Data.Xournal.Map
 
 type TLayerBBoxBuf buf = GLayerBuf buf [] StrokeBBox
 
diff --git a/src/Data/Xournal/Generic.hs b/src/Data/Xournal/Generic.hs
--- a/src/Data/Xournal/Generic.hs
+++ b/src/Data/Xournal/Generic.hs
@@ -201,6 +201,19 @@
 
 ---- 
 
+-- |
+
 emptyPageFromOldPage :: (GListable s) => GPage b s a -> GPage b s a
 emptyPageFromOldPage p = GPage (get g_dimension p) (get g_background p) (gFromList [] )
 
+----
+
+-- | 
+
+printLayerStructureInPage :: (GListable s) => 
+                              GPage b s (GLayerBuf buf [] a) -> IO () 
+printLayerStructureInPage page = do 
+  let lyrs = get g_layers page 
+      lst = fmap (Prelude.length . get g_bstrokes) (gToList lyrs)
+  (Prelude.putStrLn . ("num of layers = "++) . show . Prelude.length . gToList ) lyrs 
+  Prelude.putStrLn $ "layer strokes = " ++ show lst 
diff --git a/xournal-types.cabal b/xournal-types.cabal
--- a/xournal-types.cabal
+++ b/xournal-types.cabal
@@ -1,5 +1,5 @@
 Name:		xournal-types
-Version:	0.3.1
+Version:	0.3.2
 Synopsis:	Data types for programs for xournal file format
 Description: 	Xournal file format data type including generic interface
 License: 	BSD3