-- 4.
lookUp :: Char -> [(Char, Char)] -> Char
lookup c [] = []
lookUp c  (x,y):(xs,ys) | c==x = y : lookUp c (xs,ys)
                        | c/=x = lookUp c (xs,ys)

-- 5.
encipher :: Int -> Char -> Char
encipher n c = lookUp c (makeKey n)
-}
-- 6.
normalize :: String -> String
normalize (xs)  = [toUpper x | x <- xs, isAlpha x || isDigit x]

-- 7.
encipherStr :: Int -> String -> String
encipherStr = undefined

-- 8.
reverseKey :: [(Char, Char)] -> [(Char, Char)]
reverseKey (x,y):(xs,ys) = (y,x) : reverseKey [(xs,ys)]