"Any" Subset Sum. Is it hard? Here is a variant of the classic partition problem: Given a list of integers can it be partitioned into $S_1$, $S_2$, and $S_3$, with $S_1$ and $S_2$ nonempty, so the sum of elements in $S_1$ equals the sum of elements in $S_2$?

Is this problem NP-hard?
The problem is known to be NP-complete: On the equal-subset-sum problem, Woeginger and Yu, IPL'92.