In reply to kernalmode1:
item.index is not a random variable, it is an iterator that goes from 0…15.
cnum.sum with (int'(item.index%2?item:0)
is equivalent to
int'(0%2 ? csum[0] : 0) + int'(1%2 ? csum[1] : 0) + int'(2%2 ? csum[2] : 0) + ... +int'(15%2 ? csum[15] : 0)
which reduces to the following constraint
int'(csum[1]) + int'(csum[3]) + int'(csum[5]) + ...int'(csum[15])) = 8
That leaves csum[0], csum[2], csum[4], … csum[14] unconstrained.