  Given a sequence converging to zero, we consider the set of numbers which are
sums of (infinite, finite, or empty) subsequences. When the original sequence
is not absolutely summable, the subsum set is an unbounded closed interval
which includes zero. When it is absolutely summable the subsum set is one of
the following: a finite union of (nontrivial) compact intervals, a Cantor set,
or a "symmetric Cantorval".
