A set is sum-free if no two (not necessarily distinct) elements when added together are part of the set itself.
For example, {1, 5, 7} is sum-free, because all members are odd, and two odd numbers when added together are always even. On the other hand, {2, 4, 9, 13} is not sum-free, as either 2 + 2 = 4 or 4 + 9 = 13 add together to a member of the set.
Write a program or function that takes a set as input, and outputs a Truthy value if the set is sum-free, and Falsy otherwise.
Examples:
Sum-free:
{}
{4}
{1, 5, 7}
{16, 1, 4, 9}
Not sum-free:
{0}
{1, 4, 5, 7}
{3, 0}
{16, 1, 4, 8}