elem :: Int -> [Int] -> Bool
-- testing 360 combinations of argument values
-- pruning with 40/53 rules
-- 2 candidates of size 1
-- 0 candidates of size 2
-- 0 candidates of size 3
-- 0 candidates of size 4
-- 4 candidates of size 5
-- 0 candidates of size 6
-- 0 candidates of size 7
-- 16 candidates of size 8
-- tested 19 candidates
elem x []  =  False
elem x (y:xs)  =  elem x xs || x == y

set :: [Int] -> Bool
-- testing 360 combinations of argument values
-- pruning with 41/52 rules
-- 2 candidates of size 1
-- 0 candidates of size 2
-- 0 candidates of size 3
-- 1 candidates of size 4
-- 0 candidates of size 5
-- 0 candidates of size 6
-- 2 candidates of size 7
-- 4 candidates of size 8
-- tested 6 candidates
set []  =  True
set (x:xs)  =  set xs && not (elem x xs)