2.1)
sum2 []  = []
sum2 [a] = []
sum2 (a:b:bs) = a+b : sum2(b:bs)

2.2)
longestseq xs = longest (seqs xs)

longest [] = []
longest (x:xs) = f x xs
  where f x [] = x
        f x (a:as) | length x >= length a = f x as
                   | otherwise = f a as

seqs [] = []
seqs xs = z : drop (length z) xs
  where z = oneasseq xs

oneasseq [] = []
oneasseq [a] = [a]
oneasseq (a:b:bs) | a <= b = a:oneasseq (b:bs)
              | otherwise = [a]

3.1)
dir a xs = [y | (x,y) <- xs, x == a] 

3.2) 
indir xs a = dirsa ++ concat (map (indir xs) dirsa)
  where dirsa = dir a xs

3.3)
indircicl xs a = indirc [] xs a

indirc acc xs a = dirsa ++ concat (map (indirc (acc ++ dirsa) xs) dirsa)
  where dirsa = (dir a xs)\\acc

5)
merge [] xs = xs
merge xs [] = xs
merge (x:xs) (y:ys) | x == y = x+y : merge xs ys
                    | x < y = x:merge xs (y:ys)
                    | x > y = y:merge (x:xs) ys

6) 
f find list | length zs >= 1 = True
            | otherwise      = False
  where zs = filter (==find) ys
        ys = splitin (length find) list

splitin n [] = []
splitin n xs = take n xs : splitin n (tail xs)