rotCenter f = (\x -> -(f (-x)))

data Answer = Yes | No | Unknown

xor :: Answer -> Answer -> Answer

xor _ Unknown = Unknown
xor Unknown _ = Unknown
xor Yes Yes = No
xor No No = No
xor _ _ = Yes

role :: Int -> [a] -> [a]
role x (y:ys)
	| x==0 = (y:ys)
	| otherwise = (role (x-1) (ys ++ [y]))

compact [] = []
compact (x:xs) = x:(compact (dropWhile (x==) xs))