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import Data.List (elemIndex)
import Data.Maybe (fromJust)
spin n xs = let (ys, zs) = splitAt n xs in zs ++ ys
exchange m n xs
| n > m = ys ++ [y] ++ zs ++ [x] ++ ws
| n == m = xs
| otherwise = exchange n m xs
where (ys, x:xs') = splitAt m xs
(zs, y:ws) = splitAt (n - m - 1) xs'
partner x y xs = exchange m n xs
where m = fromJust $ elemIndex x xs
n = fromJust $ elemIndex y xs
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