Lab 4

[BertLisser]

Exercise 2 and 3
The random set generator is missing

Exercise 6

(@@) :: Eq a => Rel a -> Rel a -> Rel a
(Set r) @@ (Set s) = Set $ nub [ (x,z) | (x,y) <- r, (w,z) <- s, y == w ]

is wrong. Must be

(@@) :: Eq a => Rel a -> Rel a -> Rel a
(Set r) @@ (Set s) = Set $ sort.nub [ (x,z) | (x,y) <- r, (w,z) <- s, y == w ]

This error makes also this definition wrong

trClos :: Ord a => Rel a -> Rel a
trClos set = apprx [foldl1 unionSet (take n rs) | n <- [1..]] 
           where rs             = iterate (set @@) set
                 apprx (x:y:zs) = if x == y then x else apprx (y:zs)

The call of sort is missing

Exercise 7
The property that the transitive closure is minimal is missing.

This is a nice idea:

-- Define Rel as a Set, to keep using Set operations and to be able to use the above implemented
-- operations.

A pity that sort was forgotten.