/prog/ challenge

A set of integers is sum-free when addition always gets you out of the set (i.e. x + y = z has no solutions -- in other words S + S and S are disjoint). Formally, let S be a subset of N. S is sum-free if for all a,b in S, a+b is not in S.

Now, let S be any set of nonzero integers. Find a subset of size > |S|/3.

You may use your favorite lisp language.

I've got a really nice solution for this one.

>>8
Checking every possible solution barely constitutes an algorithm.