import Prelude hiding (concat)
concat :: [[a]] -> [a]
concat xss = [x | xs <- xss, x <- xs]
concatt :: [[[a]]] -> [a]
concatt xsss = [x| xss<- xsss, xs <- xss, x <- xs]
{-
concatt [[[1],[2]]]
[1,2]
-}
-- factors :: Int -> [Int]
factors n = [x | x <- [1..n], n `mod` x == 0]
pairs :: [a] -> [(a,a)]
pairs xs = zip xs (tail xs)
sorted xs = and [x<=y | (x,y) <- pairs xs]