nbody_orig_1.chpl   : currently one of Albert's two best; stores Planet as class
                      note: uses zippered iteration (as do all of these?)

nbody_record_2.chpl : other best; changes Planet from class to record

nbody_record_domain_2a.chpl : (a) uses explicit domain in formal arguments
                              (b) uses domain literal in for loops

nbody_forloop_3.chpl : iterates over an array slice rather than a range

nbody_vector_4.chpl : 3-tuples represented using array rather than scalars

nbody_rangesub_5.chpl : like vector but named the ranges

nbody_reductions_6.chpl : uses reductions across 3-element vectors

nbody_iterator_7.chpl : uses a triangular iterator to express the n^2 ops
