elem :: Int -> [Int] -> Bool
-- testing 360 combinations of argument values
-- pruning with 44/57 rules
-- looking through 2 candidates of size 1
-- looking through 3 candidates of size 2
-- looking through 5 candidates of size 3
-- looking through 20 candidates of size 4
-- looking through 48 candidates of size 5
-- looking through 75 candidates of size 6
-- looking through 149 candidates of size 7
-- looking through 368 candidates of size 8
-- tested 396 candidates
elem x []  =  False
elem x (y:xs)  =  elem x xs || x == y

set :: [Int] -> Bool
-- testing 360 combinations of argument values
-- pruning with 46/57 rules
-- looking through 2 candidates of size 1
-- looking through 2 candidates of size 2
-- looking through 5 candidates of size 3
-- looking through 11 candidates of size 4
-- looking through 20 candidates of size 5
-- looking through 41 candidates of size 6
-- looking through 100 candidates of size 7
-- looking through 234 candidates of size 8
-- tested 200 candidates
set []  =  True
set (x:xs)  =  set xs && not (elem x xs)