diff --git a/3or4/Interpreter/Haskell.hs b/3or4/Interpreter/Haskell.hs
index 4ac06a5..71e4c51 100644
--- a/3or4/Interpreter/Haskell.hs
+++ b/3or4/Interpreter/Haskell.hs
@@ -10,14 +10,14 @@ import Control.Monad.Identity ( Identity( runIdentity ) )
 subst :: Variable -> Exp -> Exp -> Exp
 subst var e = \case
   Apply e1 e2 -> Apply (subst var e e1) (subst var e e2)
-  Lambda x e' -> Lambda x $ if var /= x then subst var e e' else e'
+  Lambda x e' -> Lambda x $ if var == x then e' else subst var e e'
   Var x -> if var == x then e else Var x
   Const c es -> Const c $ map (subst var e) es
-  Rec x e' -> Rec x $ if var /= x then subst var e e' else e'
+  Rec x e' -> Rec x $ if var == x then e' else subst var e e'
   Case e' bs -> Case (subst var e e') $ map substBr bs
     where
       substBr :: Br -> Br
-      substBr (Branch c vs e') = Branch c vs $ if var `notElem` vs then subst var e e' else e'
+      substBr (Branch c vs e') = Branch c vs $ if var `elem` vs then e' else subst var e e'
 
 -- Task 5
 eval :: Exp -> Exp
@@ -39,7 +39,7 @@ eval = runIdentity . eval'
       x -> pure x
     
     lookupBranch :: Constructor -> [Br] -> Identity ([Variable], Exp)
-    lookupBranch c [] = error "No matching branch"
+    lookupBranch c [] = error $ "No matching branch, c was: " <> show c
     lookupBranch c ((Branch c' bs e):brs) =
       if c == c'
       then pure (bs,e)