-- <PRE>
plusone x = x + 1

lastone = head . reverse
prefix = reverse . tail . reverse

mymap f l = [ f x | x <- l]

myfilter f l = [ x | x <- l, f x]

absolute x | x < 0 = -x
           | x >= 0 = x

myand :: Bool -> Bool -> Bool
myand True False = False
myand True True = True
myand False False = False
myand False True = False

myand2 True True = True
myand2 x y = False

hd (x:xs) = x
tl (x:xs) = xs

firstOfThree [x,y,z] = x

plus :: Int -> Int -> Int
plus x y = if x == 0 then y else 1 + (plus (x-1) y)

len [] = 0
len (x:xs) = 1 + (len xs)

len2 [] = 0
len2 (x:xs) = 1 + z where z = len2 xs

choose x y z = if x then y else z
difference x y = x - y

k x y = x

sort                :: Ord a => [a] -> [a]
sort                 = foldr insert []

insert              :: Ord a => a -> [a] -> [a]
insert x []          = [x]
insert x (y:ys)
        | x <= y     = x:y:ys
        | otherwise  = y:insert x ys
-- </PRE>