We express the amplitudes for charmless three-body B decays in terms of
diagrams. In addition, we show how to use Dalitz-plot analyses to obtain decay
amplitudes which are symmetric or antisymmetric under the exchange of two of
the final-state particles. When annihilation-type diagrams are neglected, as in
two-body decays, many of the exact, purely isospin-based results are modified,
leading to new tests of the standard model (SM). Some of the tests can be
performed now, and we find that present data agree with the predictions of the
SM. Furthermore, contrary to what was thought previously, it is possible to
cleanly extract weak-phase information from three-body decays, and we discuss
methods for B -> K pi pi, K K Kbar, K Kbar pi and pi pi pi.Comment: 30 pages, 10 figures, reference updated, sentences added regarding
indirect CP violation and CP of the final state. Significant text added
describing how to obtain symmetric/antisymmetric decay amplitudes, results of
the comparison of the predictions of the SM with present data for several
decays, and the momentum dependence of the diagram