Indentation error

Indentation.hs

type Title = String
type Author = String
data Product = Book Title Author
                   | Video Author
                   | CD Title Integer Author
                   deriving (Eq,Show)

getTitle (Book title _ ) = title
getTitle (Video title  )  = title
getTitle (CD title _ _ )  =title

getTitles l = map (\x->getTitle x) l
lookupTitle _ [] = Nothing
lookupTitle x (y:ys) | getTitle y==x = Just y
                     |otherwise = lookupTitle x ys

lookupTitles a b = map (\x->lookupTitle x b) a

bookAuthors l = filter author l
  where author (Book _ _) = True
        author _ = False