(?) :: Int -> Int -> Int
-- testing 360 combinations of argument values
-- pruning with 0/0 rules
-- 4 candidates of size 1
-- 0 candidates of size 2
-- 24 candidates of size 3
-- tested 6 candidates
x ? y  =  x + y

(?) :: Int -> Int -> Int
-- testing 360 combinations of argument values
-- pruning with 0/0 rules
-- 4 candidates of size 1
-- 0 candidates of size 2
-- 24 candidates of size 3
-- tested 18 candidates
x ? y  =  x * y

i :: Int -> Int
-- testing 360 combinations of argument values
-- pruning with 0/0 rules
-- 3 candidates of size 1
-- 0 candidates of size 2
-- 10 candidates of size 3
-- tested 6 candidates
i x  =  x + 1

d :: Int -> Int
-- testing 360 combinations of argument values
-- pruning with 0/0 rules
-- 3 candidates of size 1
-- 0 candidates of size 2
-- 10 candidates of size 3
-- tested 13 candidates
d  =  undefined  -- search exhausted
-- could not find implementation using only
-- 0, 1, (+), and (*)
-- consider increasing target/maxSize or refining the ingredients

