factorial :: Int -> Int
-- testing 4 combinations of argument values
-- pruning with 27/65 rules
-- looking through 3 candidates of size 1
-- looking through 3 candidates of size 2
-- looking through 7 candidates of size 3
-- looking through 13 candidates of size 4
-- looking through 35 candidates of size 5
-- looking through 61 candidates of size 6
-- looking through 219 candidates of size 7
-- tested 153 candidates
factorial 0 = 1
factorial x = x * factorial (x - 1)
factorial :: Int -> Int
-- testing 4 combinations of argument values
-- pruning with 32/72 rules
-- looking through 3 candidates of size 1
-- looking through 3 candidates of size 2
-- looking through 7 candidates of size 3
-- looking through 13 candidates of size 4
-- looking through 35 candidates of size 5
-- looking through 101 candidates of size 6
-- tested 89 candidates
factorial x = foldr (*) 1 [1..x]