diff --git a/app/Main.hs b/app/Main.hs
index 2385f93..3969ca5 100644
--- a/app/Main.hs
+++ b/app/Main.hs
@@ -1,8 +1,14 @@
 module Main where
 
+import Control.Lens
+import Data.Either
 import Petzval.Optics
 import Petzval.Optics.RTM
 import Petzval.System
+import Petzval.Trace
+import Petzval.Calculations
+import Linear
+import Numeric.AD.Mode (Scalar, Mode)
 
 bk7 = SellemeierMat [ (1.03961212,  6.00069867e-3 )
                     , (0.231792344, 2.00179144e-2 )
@@ -34,6 +40,22 @@ system2 =
   where s_sk16 = ConstMat 1.620408
         s_f4 = ConstMat 1.616589
 
+merit :: (Material mat, RealFloat a, Scalar a ~ Double, Epsilon a, Mode a) => [Element mat a] -> a
+-- merit :: (Material mat) => [Element mat Double] -> Double
+merit system = result 
+  where baked = bake 0.587618 system
+        ep = entrancePupil baked
+        result = sum
+          . map (^2)
+          . map (\ angle -> rmsSize
+                  . toListOf (each._pos._xy)
+                  -- . (\x -> x :: [Ray a])
+                  . rights
+                  . map fst
+                  . map (raytrace baked . createRay Nothing ep angle)
+                  $ spiralPattern 100)
+          $ [0, 7.07, 15]
+
 main :: IO ()
 main =
   let baked = bake 0.587618 system2
diff --git a/flake.nix b/flake.nix
index ae6b274..4be0ecd 100644
--- a/flake.nix
+++ b/flake.nix
@@ -18,6 +18,7 @@
         devShell = pkgs.mkShell {
           buildInputs = with pkgs; [
             cabal-install
+            haskell-language-server
             ghc
           ];
         };
diff --git a/lib/Petzval/Internal/Vec.hs b/lib/Petzval/Internal/Vec.hs
index 2f8e44e..9ed0529 100644
--- a/lib/Petzval/Internal/Vec.hs
+++ b/lib/Petzval/Internal/Vec.hs
@@ -25,7 +25,7 @@ class VConcat (v1 :: * -> *) (v2 :: * -> *) where
   type VConcated v1 v2 :: * -> *
   vconcat :: v1 a -> v2 a -> (VConcated v1 v2) a
 
-instance {-# OVERLAPPED #-}  VConcat V0 v where
+instance VConcat V0 v where
   type VConcated V0 v = v
   vconcat V0 v = v
 
diff --git a/lib/Petzval/System.hs b/lib/Petzval/System.hs
index a868760..49c8b68 100644
--- a/lib/Petzval/System.hs
+++ b/lib/Petzval/System.hs
@@ -34,7 +34,7 @@ pupil (stop@Stop{_outsideRadius}) subsystem =
            , position = -cy / cu }
 
 -- | Compute the entrance pupil of a system viewed from infinity
-entrancePupil :: (RealFloat a, Mode a, Scalar a ~ Double, Epsilon a, Show a) => [Element BakedIOR a] -> Pupil a
+entrancePupil :: (RealFloat a, Mode a, Scalar a ~ Double, Epsilon a) => [Element BakedIOR a] -> Pupil a
 entrancePupil system = pupil stop prefix
   where (prefix, (Just stop), _) = splitSystem system
 
@@ -73,9 +73,9 @@ instance Num a => Monoid (Seidel a) where
 
 
 -- | Initial matrix is [ h_ h; u_ u ]
-seidel' :: (RealFloat a, Mode a, Scalar a ~ Double, Epsilon a, Show a) => M22 a -> Element BakedIOR a -> (M22 a, Seidel a)
+seidel' :: (RealFloat a, Mode a, Scalar a ~ Double, Epsilon a) => M22 a -> Element BakedIOR a -> (M22 a, Seidel a)
 seidel' rays (s@Stop{}) = (thicknessRTM s !*! rays, mempty)
-seidel' rays (s@Surface{_material=BakedIOR n1 n2,_roc=roc}) = Debug.Trace.trace msg (rays'', Seidel {sphr,coma,asti,fcur,dist})
+seidel' rays (s@Surface{_material=BakedIOR n1 n2,_roc=roc}) = (rays'', Seidel {sphr,coma,asti,fcur,dist})
   where rays' = refractionRTM s !*! rays
         rays'' = thicknessRTM s !*! rays'
         marg = column _y
@@ -97,13 +97,12 @@ seidel' rays (s@Surface{_material=BakedIOR n1 n2,_roc=roc}) = Debug.Trace.trace
         -- However, a is 0 whenever the marginal ray is normal to the surface
         -- Thus, we use this formula from Kidger
         dist = -abar^3 * h * δ1n2 + (rays^. chief._x) * abar * (2 * h * abar - rays ^. chief._x * a) * δ1n / roc
-        msg = intercalate "\t" [show δun, show a, show abar]
         -- TODO: evaluate at other IORs
         -- cbas = h  (n2 - n1) / n1
         -- c1 = 
         
 -- | Compute the seidel coefficients of a system given the pupil and field angle
-seidel :: (RealFloat a, Mode a, Scalar a ~ Double, Epsilon a, Show a) => Pupil a -> Double -> [Element BakedIOR a] -> [Seidel a]
+seidel :: (RealFloat a, Mode a, Scalar a ~ Double, Epsilon a) => Pupil a -> Double -> [Element BakedIOR a] -> [Seidel a]
 seidel pupil fieldAngle =
   snd . mapAccumL seidel' rays
   where ubar = auto (tan (pi / 180 * fieldAngle))
diff --git a/petzval-hs.cabal b/petzval-hs.cabal
index 834987a..45aed00 100644
--- a/petzval-hs.cabal
+++ b/petzval-hs.cabal
@@ -35,6 +35,9 @@ executable petzval-hs
     -- LANGUAGE extensions used by modules in this package.
     -- other-extensions:
     build-depends:    base   ^>=4.15.1.0,
+                      ad     ^>=4.5.2,
+                      linear ^>=1.21,
+                      lens   ^>=5.2,
                       petzval-hs
     hs-source-dirs:   app
 
@@ -46,6 +49,7 @@ library
         Petzval.Optics.RTM
         Petzval.System
         Petzval.Trace
+        Petzval.Calculations
     other-modules:
         Petzval.Internal.Vec
     hs-source-dirs: lib