dreieck.hs

import Data.List

newline [a]      = []
newline (a:b:xs) = abs (a-b) : (newline (b:xs))

check prev []   = True
check prev line = all (`notElem` prev) line && nub line == line && check (line ++ prev) (newline line)

main = print $ filter (check []) $ concatMap permutations $ filter ((==5) . length) $ subsequences [1..15]