[...| xs = [0..n], ...]

[S.D.Mechveliani]

I wrote    f n = [(x,y,z,u) | xs = [0..n],  x <- xs,
                              ys = xs\\[x], y <- ys,
                              zs = ys\\[y], z <- zs,  u <- zs\\[z]
                 ],

and  Gofer  allowed this. But  Haskell-98  does not.
So, i write here
                         ...  xs <- [[0..n]],  x <- xs,
                              ys <- [xs\\[x]], y <- ys  ...

This is like saying        `X belongs to the set of hat owners'
instead of                 `X has a hat'.
Is there a nicer way out?
Thank you in advance for your advices.

------------------
Sergey Mechveliani
[EMAIL PROTECTED]