strings :: Int -> [ String ]
strings 0 = [""]
strings n = concat ( map (\ x -> map (\ tail -> x : tail ) tails ) ['a'.. 'z'])
            where tails = strings (n -1)

paliTest :: String -> Bool
paliTest "" = True
paliTest a = (a == reverse a)

paliListN :: [String] -> [String]
paliListN (x:xs)= if(paliTest x) then x:paliListN xs
                  else paliListN xs