diff --git a/HGE2D.cabal b/HGE2D.cabal
--- a/HGE2D.cabal
+++ b/HGE2D.cabal
@@ -2,7 +2,7 @@
 --  see http://haskell.org/cabal/users-guide/
 
 name:                HGE2D
-version:             0.1.6.5
+version:             0.1.7.1
 synopsis:            2D game engine written in Haskell
 description:         See README and examples/ for further information
 license:             MIT
@@ -43,7 +43,9 @@
       base >= 4.9.0.0 && < 5.0,
       OpenGL >=3.0 && < 3.1,
       GLUT >= 2.7 && < 2.8,
-      time >= 1.5.0.1 && < 1.7
+      time >= 1.5.0.1 && < 1.7,
+      safe == 0.3.9,
+      deepseq == 1.4.2.0
   hs-source-dirs:      src
   default-language:    Haskell2010
   ghc-options:         -O2 -W -fwarn-incomplete-patterns
diff --git a/src/HGE2D/Engine.hs b/src/HGE2D/Engine.hs
--- a/src/HGE2D/Engine.hs
+++ b/src/HGE2D/Engine.hs
@@ -12,7 +12,8 @@
 import HGE2D.Time
 import HGE2D.Render ()
 
-import Control.Concurrent (newMVar, readMVar, takeMVar, putMVar, MVar)
+import Control.Concurrent (newMVar, readMVar, takeMVar, putMVar, swapMVar, MVar)
+import Control.DeepSeq
 import Graphics.UI.GLUT
 
 --------------------------------------------------------------------------------
@@ -85,7 +86,7 @@
 -- | Mouse hover interactions with the engine
 mouseHover :: EngineState a -> MVar (a) -> Position -> IO ()
 mouseHover es mvarGs (Position x y) = do
-    gs <- takeMVar mvarGs ---TODO rename
+    gs <- readMVar mvarGs ---TODO rename
 
     let w          = fst $ getSize es gs
         h          = snd $ getSize es gs
@@ -93,7 +94,7 @@
         correctedY = (realToFrac y) * (snd $ getSize es gs) / h
         newState   = hover es correctedX correctedY gs
 
-    putMVar mvarGs newState
+    swapMVar mvarGs newState
     return ()
 
 
@@ -110,7 +111,7 @@
 -- | MouseDown interaction with the engine
 mouseDown :: EngineState a -> MVar (a) -> GLint -> GLint -> IO ()
 mouseDown es mvarGs x y = do
-    gs <- takeMVar mvarGs ---TODO rename
+    gs <- readMVar mvarGs ---TODO rename
 
     ---TODO define method for corrections since used here and in hover
     let w          = fst $ getSize es gs
@@ -119,13 +120,13 @@
         correctedY = (realToFrac y) * (snd $ getSize es gs) / h
         newState   = click es correctedX correctedY gs
 
-    putMVar mvarGs newState
+    swapMVar mvarGs newState
     return ()
 
 -- | MouseUp interaction with the engine
 mouseUp :: EngineState a -> MVar (a) -> GLint -> GLint -> IO ()
 mouseUp es mvarGs x y = do
-    gs <- takeMVar mvarGs ---TODO rename
+    gs <- readMVar mvarGs ---TODO rename
 
     ---TODO define method for corrections since used here and in hover
     let w          = fst $ getSize es gs
@@ -134,7 +135,7 @@
         correctedY = (realToFrac y) * (snd $ getSize es gs) / h
         newState   = mUp es correctedX correctedY gs
 
-    putMVar mvarGs newState
+    swapMVar mvarGs newState
     return ()
 
 --------------------------------------------------------------------------------
@@ -142,7 +143,7 @@
 -- | KeyPress interaction with the engine
 keyDown :: EngineState a -> MVar (a) -> GLint -> GLint -> Char -> IO ()
 keyDown es mvarGs x y c = do
-    gs <- takeMVar mvarGs ---TODO rename
+    gs <- readMVar mvarGs ---TODO rename
 
     ---TODO define method for corrections since used here and in hover
     let w          = fst $ getSize es gs
@@ -151,13 +152,13 @@
         correctedY = (realToFrac y) * (snd $ getSize es gs) / h
         newState   = kDown es correctedX correctedY c gs
 
-    putMVar mvarGs newState
+    swapMVar mvarGs newState
     return ()
 
 -- | KeyRelease interaction with the engine
 keyUp :: EngineState a -> MVar (a) -> GLint -> GLint -> Char -> IO ()
 keyUp es mvarGs x y c = do
-    gs <- takeMVar mvarGs ---TODO rename
+    gs <- readMVar mvarGs ---TODO rename
 
     ---TODO define method for corrections since used here and in hover
     let w          = fst $ getSize es gs
@@ -166,7 +167,7 @@
         correctedY = (realToFrac y) * (snd $ getSize es gs) / h
         newState   = kUp es correctedX correctedY c gs
 
-    putMVar mvarGs newState
+    swapMVar mvarGs newState
     return ()
 
 --------------------------------------------------------------------------------
@@ -174,12 +175,12 @@
 -- | Idle function of the engine. Used to e.g. apply changes in time to the game state
 idle :: EngineState a -> MVar (a) -> IdleCallback
 idle es mvarGs = do
-  gs   <- takeMVar mvarGs
+  gs <- readMVar mvarGs
   secs <- getSeconds
 
   let ms       = toMilliSeconds secs
       deltaMs  = ms - (getTime es gs)
       newState = moveTime es deltaMs (setTime es ms gs) ---TODO currently bot setting the time AND transforming
 
-  putMVar mvarGs newState
+  deepseq newState (swapMVar mvarGs newState)
   postRedisplay Nothing
diff --git a/src/HGE2D/Geometry.hs b/src/HGE2D/Geometry.hs
--- a/src/HGE2D/Geometry.hs
+++ b/src/HGE2D/Geometry.hs
@@ -14,6 +14,8 @@
 import HGE2D.Datas
 import HGE2D.Classes
 
+import Safe
+
 ---TODO rewrite most / all functions to use classes
 ---TODO use typedefs
 
@@ -60,12 +62,12 @@
     p2 = getPos y
 
 -- | Find the closest in [b] to a
-closest :: (Positioned a, Positioned b) => a -> [b] -> b
-closest a bs = minimumBy (  \ x y -> compare (distanceSqr a x) (distanceSqr a y)  ) bs
+closest :: (Positioned a, Positioned b) => a -> [b] -> Maybe b
+closest a bs = minimumByMay (  \ x y -> compare (distanceSqr a x) (distanceSqr a y)  ) bs
 
 -- | Find the furthest in [b] to a
-furthest :: (Positioned a, Positioned b) => a -> [b] -> b
-furthest a bs = maximumBy (  \ x y -> compare (distanceSqr a x) (distanceSqr a y)  ) bs
+furthest :: (Positioned a, Positioned b) => a -> [b] -> Maybe b
+furthest a bs = minimumByMay (  \ x y -> compare (distanceSqr a x) (distanceSqr a y)  ) bs
 
 -- | Given a position and projectile speed of a gun / turret and an object defined by its current position and velocity
 --   Calculates the position where both will intercept. (useful for pre-aiming)
@@ -121,11 +123,21 @@
     newY = (snd $ bbMin bb) + (height / 2)
     (width, height) = sizeBB bb
 
----TODO make monoid
 
+-- | Testing whether a BoundingBox has the same min and max values
+isNullBB :: BoundingBox -> Bool
+isNullBB bb = (bbMin bb) == (bbMax bb)
+
+-- | A BoundingBox which counts as null, having the same min and max position
+nullBB :: BoundingBox
+nullBB = BoundingBox (0,0) (0,0)
+
 -- | Merges two bounding boxes, creating a new one which wraps around the inputs
+--   In case a nullBB is passed as one parameter, the other BoundingBox is returned
 mergeBB :: BoundingBox -> BoundingBox -> BoundingBox
-mergeBB bb1 bb2 = BoundingBox newMin newMax
+mergeBB bb1 bb2 | isNullBB bb1 = bb2
+                | isNullBB bb2 = bb1
+                | otherwise    = BoundingBox newMin newMax
   where
     newMin = mergeMin (bbMin bb1) (bbMin bb2)
     newMax = mergeMax (bbMax bb1) (bbMax bb2)
diff --git a/src/HGE2D/Instances.hs b/src/HGE2D/Instances.hs
--- a/src/HGE2D/Instances.hs
+++ b/src/HGE2D/Instances.hs
@@ -17,6 +17,13 @@
 
 --------------------------------------------------------------------------------
 
+-- | Instance of Monoid for BoundingBox
+instance Monoid BoundingBox where
+    mempty = nullBB
+    mappend = mergeBB
+
+--------------------------------------------------------------------------------
+
 -- | Instance of HasBoundingBox for BoundingBox
 instance HasBoundingBox BoundingBox where
     getBB = id