diff --git a/Algebra/Vector.hs b/Algebra/Vector.hs
index abcab5d..7bdc9c4 100644
--- a/Algebra/Vector.hs
+++ b/Algebra/Vector.hs
@@ -11,11 +11,11 @@ import MyPrelude
 
 
 -- |Checks whether the Point is in a given dimension.
-inRange :: Coord -- ^ X dimension
-        -> Coord -- ^ Y dimension
-        -> PT    -- ^ Coordinates
-        -> Bool  -- ^ result
-inRange (xlD, xuD) (ylD, yuD) p = x <= xuD && x >= xlD && y <= yuD && y >= ylD
+inRange :: Square -- ^ the square, defined by x/y dimensions
+        -> PT     -- ^ Coordinate
+        -> Bool   -- ^ result
+inRange ((xlD, xuD), (ylD, yuD)) p =
+  x <= xuD && x >= xlD && y <= yuD && y >= ylD
   where
     (x, y) = unp2 p
 
diff --git a/Algebra/VectorTypes.hs b/Algebra/VectorTypes.hs
index d6934bc..0f64f4b 100644
--- a/Algebra/VectorTypes.hs
+++ b/Algebra/VectorTypes.hs
@@ -9,6 +9,7 @@ type Vec     = R2
 type PT      = P2
 type Coord   = (Double, Double)
 type Segment = (PT, PT)
+type Square  = (Coord, Coord)
 
 
 data Alignment = CW
diff --git a/Graphics/Diagram/Types.hs b/Graphics/Diagram/Types.hs
index df02049..15aec10 100644
--- a/Graphics/Diagram/Types.hs
+++ b/Graphics/Diagram/Types.hs
@@ -138,4 +138,4 @@ maybeDiag b d
 
 
 filterValidPT :: DiagProp -> [PT] -> [PT]
-filterValidPT p = filter (inRange (dX p) (dY p))
+filterValidPT p = filter (inRange (dX p, dY p))