  The recent LHCb measurements of the $B_s \to K^-\pi^+$ and $B_s \to K^+K^-$
rates and CP asymmetries are in agreement with U-spin expectations from $B_d
\to K^+\pi^-$ and $B_d \to \pi^+\pi^-$ results. We derive the complete set of
isospin, U-spin, and SU(3) relations among the CP asymmetries in two-body
charmless $B \to PP$ and $B \to PV$ decays, some of which are novel. To go
beyond the unbroken SU(3) limit, we present relations which are properly
defined and normalized to allow incorporation of SU(3) breaking in the simplest
manner. We show that there are no CP relations beyond first order in SU(3) and
isospin breaking. We also consider the corresponding relations for charm
decays. Comparing parametrizations of the leading order sum rules with data can
shed light on the applicability and limitations of both the flavor symmetry and
factorization-based descriptions of SU(3) breaking. Two factorization relations
can already be tested, and we show they agree with current data.
