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data Tree a = Empty | Branch a (Tree a) (Tree a) deriving (Show, Eq)
cbalTree :: Int -> [Tree Char]
cbalTree 0 = [Empty]
cbalTree x
| even n = [Branch 'x' lt rt | let st = cbalTree ln, lt <- st, rt <- st]
| otherwise = let st1 = cbalTree ln
st2 = cbalTree (n - ln) in
[Branch 'x' lt rt | lt <- st1, rt <- st2] ++
[Branch 'x' lt rt | lt <- st2, rt <- st1]
where ln = n `div` 2
n = x - 1
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