Rephasing Invariance and Hierarchy of the CKM Matrix
  We identified a set of four rephasing invariant parameters of the CKM matrix. They are found to exhibit hierarchies in powers of $\lambda^2$, from $\lambda^2$ to $\lambda^8$. It is shown that, at the present level of accuracy, only the first three parameters are needed to fit all available data on flavor physics. 
T.K. Kuo, Lu-Xin Liu